100 
PALAEONTOLOGY OF NEW YORK. 
In A. coriacea Linnarsson found small circular scars in the middle of this 
valve, abutting closely against the median septum. The septal characters seen 
in the two species mentioned are also shown in Walcott’s figures of A. sub- 
sidua, White/* * * § Mr. Matthew has described some features of the hinge-line as 
follows: “Just within the posterior margin [of the pedicle-valve] there are four 
minute pits, of which the two inner correspond to small tooth-like projections 
of the dorsal valve; the two outer ones are opposite the posterior ends of the 
comma-shaped grooves of the umbonal depression.”! We are not confident 
that we have been able to detect these characters satisfactorily on Mr. Mat¬ 
thew’s typical specimens, but the suggestion has already been made that with 
fossils as liable to distortion and imperfect preservation as these frail bodies, 
great caution is needed in the separation of permanent and fugitive features. 
The shell-substance in this genus is essentially corneous and, as observed by 
Linnarsson, is composed of several laminae. The surface is usually devoid of 
other ornamentation than concentric growth-lines, but in A. granulata, Linnars¬ 
son, A. subsidua, White, and A. Matthewi, Hartt, the concentric lines are more 
or less interrupted, producing a granular or papillate appearance. 
The known species of Acrothele are few, and all its American representa¬ 
tives belong to primordial faunas. In 1874, Dr. White described, under the 
name Acrotreta ? subsidua,t a species from Antelope Springs, Utah, which he 
subsequently (1880, loc. cit .) referred to Acrothele. Mr. Walcott, in 1884,§ 
referred to this genus the Lingula Matthewi of Hartt, from the St. John group,|| 
and; in the same year, described the species Acrothele ? dichotoma ,11 from the 
Prospect Mountain group of Nevada. This species, however, bears a very 
distinct subapical slope, and was subsequently transferred by its author to the 
genus Acrotreta.** Of the two species described by Linnarsson, A. coriacea 
and A. granulata, the latter has been reported by Dr. Davidson, from the Upper 
* Bulletin No. 30, United States Geological Survey, pi. ix, figs. 4 a, 4 c. 
t Transactions of the Royal Society of Canada, p. 40. 1885. 
I Geographical and Geological Exploration West of 100th Meridian : Prelim. Rept. Invert. Foss., p. 6. 
§ Bulletin No. 10, United States Geological Survey. 
| Mr. Matthew has designated two varieties of this species: (a) .priina, ( b ) lata. 
If Palaeontology Eureka District, loc. cit. 
** Bulletin No. 30, United States Geological Survey, p. 107. 
