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. Terebratula, Davidson. Quart. Journ. Geol. Soc. London, vol. xviii, p. 27, pi. ii, tigr. 1. 
1863. Terebi'atula, de Koninck. Foss. Paleoz. de I’Inde, p. 32, pi. ix, fig. 1. 
1878. Terebratula, Waagen. Records Geol. Surv. India, vol. ix, p. 186. 
1882. Hemi'ptychina, Waagen. Pi’oductus-limestone Fossils; Brachiopoda, pp. 361-375, pi. xxvi, 
figs. 6-10; pi. xxvii, figs. 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” {pp. cit, p. 361) and, un¬ 
fortunately, without citing any species 
as typical, gives, first in his list of 
descriptions a smooth shell, H. sublavis, 
Waagen. The propriety of including 
these plicated and smooth shells in the 
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 
Fig. 222. Hemiptychina Himalayensis, Davidson. 
A portion of the interior; showing tlie absence of dental 
plates in the pedicle-valve, and the DiELASMA-like 
brachidium. (Waagen.) 
