scholarly journals Agnostid trilobites from the Upper Ordovician of Sweden and Bomholm, Denmark

1989 ◽  
Vol 37 ◽  
pp. 213-226
Author(s):  
Per Ahlberg
Keyword(s):  
British Isles ◽  
Upper Ordovician ◽  
Generic Concept ◽  
South Central

Arthrorhachis tarda (Barrande, 1846) and Sphaeragnostus cingulatus (Olin, 1906) are described from the Upper Ordovician (Harjuan Series) of Sweden and Bornholm, Denmark. S. cingulatus is extremely rare, while A. tarda is generally abundant in middle Ashgillian strata and known from a great number of localities in southern and south-central Scandinavia. Outside Scandinavia, A. tarda is frequently encoun- tered in the pre-Himantian Ashgill of Poland, Bohemia, various parts of the British Isles, and Kazakh­stan. In most of these areas, the species is generally confined to mudstone sequences, and it is usually associated with faunas of Mediterranean type. The generic concept of Sphaeragnostus is revised.

On Some Species of Catillaria S. Lat. and Halecania in the British Isles

1989 ◽  
Vol 21 (3) ◽  
pp. 217-227 ◽  
Author(s):  
B. J. Coppins
Keyword(s):  
New Combinations ◽  
British Isles ◽  
Generic Concept

AbstractA broad generic concept is adopted for Catillaria, and the following new combinations made: C. aphana (Nyl.) Coppins, C. modesta (Müll. Arg) Coppins (the basionym, Lecidea modesta Müll. Arg., being lectotypified), C. picila (Massal.) Coppins, and C. scotinodes (Nyl.) Coppins. Lecidea botryiza Nyl. ex Stirton is added to the synonymy of Micarea lutulata. Catillaria rhypodiza is transferred to Halecania, and a new, sorediate, corticolous species of that genus, H. viridescens Coppins & P. James, is described.

A lower Silurian (Llandovery) diplobathrid crinoid (Camerata) from mid-Wales

2020 ◽  
Vol 157 (7) ◽  
pp. 1176-1180 ◽  
Author(s):  
Fiona E. Fearnhead ◽  
Stephen K. Donovan ◽  
Joseph P. Botting ◽  
Lucy A. Muir
Keyword(s):  
Turbidity Current ◽  
British Isles ◽  
Upper Ordovician ◽  
Environmental Fluctuation ◽  
Lower Silurian ◽  
Sedimentary Succession ◽  
Early Palaeozoic ◽  
Cover Plates

AbstractEarly Palaeozoic crinoids are known only patchily from the British Isles except for accumulations at starfish beds. A single, exquisitely preserved crinoid is reported from the Telychian (Llandovery, Silurian) of the Pysgotwr Grits Formation of the Llangurig area, Powys, mid-Wales. This sedimentary succession is turbiditic in origin and poorly fossiliferous. The crinoid is a diplobathrid camerate, Euptychocrinus longipinnulus sp. nov., preserved as an external mould without counterpart. It has a high, shuttlecock-like crown; a conical, unsculptured cup; low infrabasals; a pair of long, slender, feather-like arms on each ray, each bearing numerous long pinnules; and a heteromorphic column. Most previous reports of this genus have been from the Upper Ordovician – lower Silurian series of Laurentia; uncertainly, it is described from the Upper Ordovician deposits of Morocco (Gondwana). Euptychocrinus longipinnulus is the first Avalonian occurrence. The beautiful preservation of the arms, including cover plates of pinnules, contrasts with the proxistele, which is a series of ‘broken sticks’. This crinoid responded to an adverse environmental fluctuation, probably a turbidity current, by autotomizing the stem, but it was carried downslope and buried alive.

The morphology and ultrastructure ofBrevigraptus quadrithecatusn. gen., n. sp. (Diplograptacea), and Its convergence uponDicaulograptus hystrix(Bulman)

1988 ◽  
Vol 62 (3) ◽  
pp. 448-463 ◽  
Author(s):  
Charles E. Mitchell
Keyword(s):  
Striking Similarity ◽  
New Taxon ◽  
Cortical Tissue ◽  
Upper Ordovician ◽  
The Third ◽  
Growth Increments ◽  
South Central

Rhabdosomes ofBrevigraptus quadrithecatusn. gen., n. sp. (Lasiograptinae, Diplograptacea), from the Upper Ordovician Viola Springs Formation of south-central Oklahoma, comprise four fully developed thecae. The sicula and the first two thecae are fully sclerotized. The ultrastructure of the fusellum is unusually dense but is overlaid by a typical diplograptacean bandaged cortex. The third and fourth thecae consist of clathria covered by a cortical sheet. Lacinia are absent. The cortical sheet comprises bandages deposited in a support dominated pattern that matches expectations of the pterobranch model of peridermal secretion. Lists are fusellar derivatives and exhibit traces of fuselli-like growth increments but no continuous fusellum is present. Lists are strongly thickened with cortical tissue. The fabricational pattern employed in list construction reveals the operation of strong historical constraints during the evolutionary reduction of the fusellum.The thecal form and list architecture ofBrevigraptus quadrithecatusare nearly identical to those ofPipiograptus hesperusWhittington.Brevigraptus quadrithecatuspossesses a Pattern G astogeny and exhibits several derived astogenetic features that it shares withP. hesperusandOrthoretiolites hamiWhittington. Both thecal and astogenetic similarities suggest the new taxon is a member of the Lasiograptinae, and is closely allied to the aforementioned species.The thecae ofB. quadrithecatusexhibit striking similarity withDicaulograptus hystrix(Bulman). However, both the details of thecal construction and primordial astogeny differ markedly between these species. The thecal similarities appear to be convergent. Accordingly,D. hystrixis probably not closely allied to the Lasiograptinae.

New camerate crinoids from the Ordovician of Scotland and Wales

2002 ◽  
Vol 93 (2) ◽  
pp. 155-161 ◽  
Author(s):  
Stephen K. Donovan ◽  
Neil Gilmour
Keyword(s):  
Morphological Features ◽  
British Isles ◽  
Insufficient Information ◽  
Upper Ordovician ◽  
Filter Feeder ◽  
Middle Ordovician ◽  
Significant Addition

ABSTRACTTwo new broad-cupped camerate crinoids are reported from the Upper Ordovician (Ashgill, Rawtheyan) Lady Burn Starfish Beds of the Girvan district, Strathclyde, SW Scotland. These represent a significant addition to the limited crinoid diversity known from the Ordovician of the British Isles. The 20-armed diplobathrid Eodimerocrinites littlewoodi gen. et sp. nov. is similar to Silurian Dimerocrinites Phillips, but lacks median ray ridges and has a distinct calyx sculpture. Camerate sp. indet. differs from E. littlewoodi in the sculpture of the dorsal cup and the arrangement of the interbrachial plates, but it preserves insufficient information for it to be further classified with confidence.New specimens of the diplobathrid gen. et sp. nov. cf Botting from the Middle Ordovician (Llanvirn, Abereiddian) of central Wales, that illustrate hitherto unknown morphological features, including a distal rhizoidal holdfast and a geniculate proximal column, suggest that this species was a rheophilic filter feeder. One specimen is one of the most complete fossil crinoids known from the Ordovician of the British Isles.

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