96 



PALEONTOLOGY OF NEW YORK. 



deeply bilobed, its anterior margin and the edges of the secondary volutions 

 fimbriate. The precise value of this pectination of the ,--;..;•-., 



saddle and coils it is difficult to determine ; it appears 

 to be developed differently in different individuals. We 

 are not satisfied as to the existence of this character in 

 A. trinuclea and A. subquadrata, but in A. Dawsoni it is 

 absent. Some individuals give indication of the pectina- 

 tion of the stem and the accessory lamellae of the loop, 

 and it has been shown by Zugmayer that in Athyris 

 (Spirigera) oxycolpus, Emmrich, of the Rhaetic beds, the 

 accessory lamellae are deeply serrated, a feature coexist- 

 ing with a bilobed saddle.* 



In A. subquadrata the lateral branches of the loop are long and projected for- 

 ward at a sharp angle. In A. trinuclea, the origin of the loop is more anterior, 

 the lateral branches erect and high, the surface of the bilobed saddle being 

 close under the opposite side of the coils. Athyris Dawsoni is a very interesting 



FIG. 68. 



Pectinated loop of AthyrU 



oxycolput, Emmrich. 



(ZVOMATBB.) 



FlO. 68. FIO. 70. FIO. 71. 



The loop of AthyrU [Seminula) Dawtoni, sp. nov.; showing the variation in development of the saddle in different 

 iodiTidoaU. Fig. 70 is a view from the umbonal region of the specimen represented in Fig. 69, indicating the 

 marginal position of the accessory lamellae upon the umbonal blades. (C.) 



form occurring with most beautiful and exceptional preservation, the brachi- 

 dium being retained with the slightest incrustation of calcareous matter upon 

 it; all the rest of the shell and the filling of its interior cavity being removed. 

 In this species the loop is normally almost without a saddle; at the union of 

 the lateral branches there is a slight forward protuberance on each side, the 

 stem arising therefrom almost without angulation ; the accessory lamellae, as 

 shown in the accompanying figures, lie upon the inner edges of the primary 



* Zdomatbb, Unt«r8uchung«n ueber rhaetische Bracbiopoden ; Beitra«ge zur Palsontologie CE^sterreicb- 

 Ungams and (ies Orients, pi. iii, figs. 21-23, and p. 353, figs. 1-3. 1882. 



