BRACHIOPODA. 



97 



lamellae, and not between the primary and secondary lamellge as usual ; further- 

 more, these accessory lamellaB are very narrow.* 



While from our present knowledge the group of Seminui.a nuist be regarded as 

 confined to the Carboniferous (and Permian?) formations, there is a little species 

 in the white sandstone of Pendleton, Indiana, in a fauna having much similar- 

 ity to that of the Schoharie grit of New York, which has many of the internal 

 shell-characters of A. suhtilita. This species, Athyris Rogem,f sp. nov., occurs 

 in the condition of internal casts which show tlie form of the shell and the 

 muscular impressions as described for Seminula, the subquadrate and perforate 

 hinge-plate and the faint median septum in the brachial valve. The brachidium 

 has not been developed. No other Devonian species showing similar affinities 

 is known. 



From our present knowledge, the athyroids, of the American palaeozoic 

 faunas appeared with this form, at the opening of the Devonian age. Mr. 

 Davidson has illustrated the spirals of a Wenlock species, Terebratula laviuscula, 

 Sowerby,J which seemed to show the existence of accessory lamellae. This 

 little shell has recently been closely investigated by the Pvev. Norman Glass,§ 

 who finds that the loop forms no saddle, and that the intercalary lamellae are 



* 111 the progress of this work some shells were received from a colleclion formei-ly belonging to the Rev. 

 H, Herzbr, of Berea, Ohio, bearing the label "Athyris 

 aiiibigua, Cork, Irelaml." The specimens possess a 

 rather more transvei-se form than usual in A. ambigua, 

 and the faint cancellation of the exfoliated sui-face 

 would indicate that it was originally spinous oi- lamel- 

 lose. It is evident that the species is not A. ambigua, 

 but its specific identity is still uncertain. There is, 

 however, no species of Athyris of which the loop is 

 known, where this organ (as shown in the accompany- 

 ing figure) is so short and so closely confined to the 

 umbonal region. The lateral branches originate from 

 the pi imary lamellae with a very slight anterior curve, 

 being almost horizontal for a short distance ; the um- 

 bonal blades of the primary lamelliE are very broad, 

 beginning in an abrupt angle with the crura and hav- 

 ing a slight curvature. The saddle is entire on the 

 anterior margin and not fimbriate. 



t Named for Di-. Benjamin Rogers, of Pendleton, in recognition of his intei-est in the development of 

 the fauna of this locality. 



I British Silurian Brachiopoda, Supplement, p. 101, pi. iv, figs. 24-2(). 



§ Geological Magazine, Dec. Ill, vol. viii, p. 495. 1891. 



FIG. 72. 

 Loop of Athyris, sp. ?, Carbonilerous limestone, Cork (?). 



(C.) 



