10 



Thomas Davidson — Spiral-Bearing BracJiiopoda. 



Atrypa margin alts, Dalman. 



We are indebted to Mr. Glass for the knowledge we now possess 

 Fig. 9. with respect to the spiral appendages and 



connecting process in this remarkable 

 species. The dorsal valve does not pre- 

 sent the same degree of convexity or 

 depth observable in that of Atrypa reticu- 

 laris, so that the spirals are smaller, with 

 a lesser degree of convexity. They do 

 not show more than five convolutions, 

 these being also more widely separated 

 one from the other than is the case with 

 Linnseus's species. The principal stems, 

 as clearly seen in the two specimens 

 Atrijpa marcjinalis, developed developed by Mr. Glass, after being 

 by Eev. N. Glass. attached to the hinge-plate, are soon con- 



nected as in A. reticularis by a V-shaped lamella. The extremities 

 of the spirals are close to each other and facing the middle portion 

 of the bottom of the dorsal valve. As in Atrypa Barrandi, the two 

 principal coils are not level, but slightly higher on their inner than 

 on their outer sides. 



Mr. Glass has also shown that the outer edge of each convolution, 

 Avhether facing the lateral or frontal margins of the shell, gives off 

 numerous small spiny projections in the same manner as in many 

 examples of Spirifer, Alliyris, Waldheimia, etc. 



Atrypa Barrandi, Dav. sp. 

 During an excursion I made near Walsall in 1847, I picked up 

 several specimens of the small species imder description. Knowing 

 nothing of its interior characters, I provisionally described it as a 

 Terebratida, but subsequently I thought it might be referable to 

 Betzia, on account of Dr. Lindstrom having found that the shell was 



possessed of spiral coils. In 1879 

 Prof. James Hall, at p. 162 of the 

 Twenty-eighth Annual Keport of the 

 New York State Museum of Natural 

 History of New York, states that the 

 Bh. Barrandi seems to be very closelj'' 

 related if not identical with his Ccelo- 

 spira disparialis ; and in the same j^ear 

 Mr. Barrande, in the 5th volume of his 

 magnificent and monumental work on 

 the Silurian Fossils of Bohemia, de- 

 scribes T. Barrandi as a species of 

 Athyris, but in his figure represents 

 it with the spiral coils of an Atrypa. 

 It has however been left to Mr. Glass to entirely investigate and 

 determine the interior characters of this species, so abundant and 

 characteristic of the Wenlock Shales of Shropshire. The shell in 

 size does not exceed some four lines in length, and the same in 



Fig. 10, 



Cmlosjnra concava, after Hall. 



