BRACHIOPODA. 99 



ency to piano-convexity, the pedicle-valve being de- C-^^ 



pressed by a broad, flat sinus, and the brachial valve \^f^M^~^ ^ 



considerably elevated; the cardinal slopes are more \^kr^^==^<'^ 



or less pronounced ; the surface is smooth or with ^^^ 



sharp, concentric growth-lines, which were not pro- ''°"'' "' ^^'">«""" "''Iwaa'IenT"" 

 duced into lamellae or spines. On the interior the hinge-plate is high, the 

 anterior face being erect, the upper face subquadrate in outline and concave, 

 the posterior ftice extending considerably beyond the hinge; perforated by 

 a visceral foramen. The loop is situated pretty well back and its structure 

 is essentially like that in Athyris planosulcata ; in S. Derbyi, however, the 

 saddle of the loop, which is entire on its anterior margin, bears a median 

 septum on its summit, extending from its anterior edge to the bifurcation of 

 the stem ; a feature not elsewhere observed among the athyroids, except in 

 Kayseria. 



In several respects these characters do not permit the assimilation of forms 

 following the type of Spirigerella Derbyi, with any of the foregoing subdivisions. 

 This subgenus and Seminula include only species with smooth shells; in 

 Spirigerella the hinge-plate attained a larger size than in any other group, 

 though its structure does not differ from that of Athyris subtilita. 



It will accomplish an excellent purpose to restrict the term . Spirigerella to 

 forms having the subplano-convex contour, strongly developed cardinal slopes, 

 and the septiferous loop. As far as the first two of these features are concerned, 

 such a restriction would include all the forms embraced by Waagen in the typical 

 division of the genus (S. Derbyi, S. pralonga, S. hybrida, S. minuta, Waagen), and 

 also those referred to the group of S. numismalis {S. numismalis and 8. alata, 

 Waagen) ; while it eliminates the group of S. grandis {S. grandis, S. media, S. 

 ovoidalis, S. fusiformis, Waagen). How far the structure of the loop in the re- 

 stricted group agrees with that of S Derbyi, has yet to be demonstrated ; but 

 .ST. grandis, the only species besides S. Derbyi of which the loop is described, has 

 not this vertical septum on the saddle, nor has it, or the group it represents, 

 the contour of the closer allies of S. Derbyi, but is a more regular, elongate and 

 biconvex shell. It seems probable that this group of Indian species will 



