BRACHIOPODA. 



97 



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

 more, these accessory lamellae are very narrow.* 



While from our present knowledge the group of Seminula must 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 Yorlc, which has many of the internal 

 shell-characters of A. suhtilita. This species, Aihyris Rogersi,-f sp. nov., occurs 

 in the condition of internal casts which show the 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,! which seemed to show the existence of accessory lamellae. This 

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

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



* lu the proffpess of this work «ome shells wei-e received from a collection formerly belonging- to the Rev. 

 H. Hbrzkb, of Berea, Ohio, bearing the label "Athyrii 

 ambigua, Cork, Ireland." The specimens possess a 

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

 and the faint cancellation of the exfoliated surface 

 would indicate that it was originally spinous or lamel- 

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

 but its specitic 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 

 umlx>nal region. The lateral branches onginate from 

 the primary lamella 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 ci'ura and hav- 

 ing a slight curvature. The saddle is entire on the 

 anterior margin and not fimbriate. 



t Named for Dr. Bbsjamin Roqbrs, of Pendleton, in i-ecognition of his interest in the development of 

 the fauna of this locality. 



t British Silurian Brachiopoda, Supplement, p. 101, pi. iv, figs. 24-26. 



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



Fig. 72. 

 Loop ot Athyri>, sp. ?, Carboniferous limestone, Cork (?). 



(O.) 



