The name Nautilus clitellarius was given by J. de C. Sowerby to a Nautiloid from the Coal-measures, Coalbrookdale, Shropshire, and the description was accompanied by three figures, each representing a different specimen. In 1884 the species was included by Professor Hyatt in his new genus Ephippioceras. In 1891 Dr. A. H. Foord found a new species, Ephippioceras costatum, which was said to be “distinguished from E. clitellarium (to which it is, however, very closely related) by the character of the septa and by the surface ornaments. The septa in E. costatum do not form such an acute lobe upon the periphery as do those of E. clitellarium, and they are also a little wider apart in the former species than they are in the latter. Moreover, E. costatum is provided with prominent transverse costæ, which are strongest upon the sides of the shell where they swell out into heavy folds. These costæ are directed obliquely backwards, and cross the septa at an acute angle, passing across the periphery and forming a shallow sinus in the middle. None of the specimens in the British Museum have the test preserved, so that the ribbing has only been observed upon casts. The costæ are equally well developed upon the body-chamber and upon the septate part of the shell in the adult, but they were either very feeble or altogether absent in the young.” A re-examination of the specimens in the Museum collection shows that the separation of the two forms is quite justifiable.
Getting hooked: the role of a U-shaped body chamber in the shell of adult heteromorph ammonites
