BRACHIOPODA. 299 



present the distinctive difference lies in the nature of the exterior. This dis- 

 tinction is certainly a convenient one, but the type of structure, so far as 

 our knowledge extends, is unknown in American faunas. The type-species of 

 this genus is D. plicata, Waagen, and this is said to be its only repre- 

 sentative. 



HEMIPTYCHINA, Waagen. 1882. 



1862. Terebratvla, Davidsoit. Quart. Journ. Geol. Soc. London, vol. xviii, p. 27, pi. ii, tig. 1. 



1863. Terebratula, db Koninck. Fobs. Pal6oz. de I'lnde, p. 32, pi. ix, fig. 1. 

 1878. Terebratula, Waagbn. Records Geol. Surv. India, vol. ix, p. 186. 



1882. Hemiptychina, Waaokn. Productus-limestone Fossils ; Brachiopoda, pp. 361-376, pi. xxvi, 

 figs. 6-10; pi. xxvii, tigs. 1-9, 11. 



Dr. Waagen has found that certain plicated terebratuloids of Permo-Carbon- 

 iferous faunas do not possess dental plates. The significance of the generic 

 name above used and the nature of the author's argument, both indicate that 

 the conception of the proposed genus was based upon such plicated shells. The 

 author, however, adds that the plica- 

 tion of the exterior "is not absolutely 

 indispensable for the shells belonging 

 to the genus" {op. cit, p. 361) and, un- 

 fortunately, without citing any species 

 as typical, gives, first in his list of 



descriptions a smooth shell, H. SUbl<ZviS, Fio. 2->2. HemtptycMna mmalayenau, Davidson. 



WflAO-pn Thp nrnnrietv of inoludinff a portion of the interior; sliowiug Uie absence of dental 

 W aagen. l ne propriety OI ini^lUUlUg p,^^^ .^ ^^^ peUicIe-valve, and the DiKtASMA-Uke 



these plicated and smooth shells in the brachidiun.. (waaoek.) 



same genus appears, on certain grounds, open to objection ; and the author's 

 intention will undoubtedly be better interpreted by regarding the plicated shell, 

 Terebratula Himalayensis, Davidson, as typical of the Hemiptychina; a shell of 

 whose interior something is known and from which it is clearly evident that 

 the author's diagnosis was largely drawn. 



These plicated terebratuloids without dental plates are unknown in American 

 faunas ; but we do find a very limited representation (as yet restricted to a 



