26 
Horizon and Lincistrom, who was the first to distinguish 
this sjDecies from O. elegantula and basalis of Dalman to which it is 
allied, found it at a great many localities in Gothland. Mr. T. Davidson has 
found it at Sedgley, near Wolverhampton. Mr, Clarke’s specimen comes 
from the hanks of the Bell, and it is associated Avith Monticulipora pulcliella, 
Milne Edw. and J. Haime, in a greyish limestone. 
Genus — ATBYPA, Dalman. 
Atrypa eeticulaeis, Linnceus. 
Anomia reticularis, Linnasus, 1767, Syst. Nat., eel. xii, p. 1152. 
AtryjJa ,, Dalmau, 1827, Vet. Akad. Handl., p. 127, pi. 4, fig. 2. 
,, ,, Davidson, 187J, Mon. Brit. Sil. Bract., p. 129, pi. 14, fig. 1-22 
(see the synonymy o£ this species on the same page). 
The descrijition of this species has been done so thoroughly and its 
form is so well known that I can dispense ivitli giving the former or repro- 
ducing the second. No Palaeontologist can he mistaken in its determination. 
Among the numerous specimens I have before me some belong to the 
Silurian and the others to the Devonian. The first are usually represented 
only by internal or external impressions, in a rather soft yellowish or brownish 
shale, belonging to the Ujiper Silurian rocks of Llandovery age, as I said 
before. These specimens iverc collected at Duntroon. 
2. Atevpa? HEMisPiiAiEiCA, J. de C. Soiuerhy. 
Airy pa hemisphcerica, J. de C. Sowerby, 1839, in Murchison’s Silurian System, p. 637, pi. 
20, fig. 7. 
Leptocociia hemisphcerica, J. Hall, 1857, Eept. Eegents State Cabin at N. York, p. 33. 
Atrypa, „ Salter, 1859, in Murchison’s Siluria, p. 100, fig. 4, and pi. 9, 
fig. 3. 
,, ,, Davidson, 1871, Mon. Brit. Sil. Brach., p. 136, pi. 13, fig. 23-30. 
This little species, siiltorhicular in shape, usually a little broader than 
long, h;is the ttvo valves unequally arched. The ventral aMvc is hemisjthse- 
rical, pretty regularly arched ; the beak is small, pointed, in-curved, and 
open [perforate]. The dorsal valve is almost flat and slightly depressed 
