1898-1902, No. 32.] FOSSIL FAUNAS FROM SERIES B. 25 



The surface shows numerous lines of growth which are strong in 

 the larger specimens, particularly near the front. The shell substance 

 is fibrous. 



The small specimens usually show on the whole a much broader, 

 more circular outline than mature ones and are always thinner and 

 flatter. A distinct, often ridge like, elevation is to be seen from the beak 

 and half way forwards. 



This form and the few related ones, that are known, are rendered 

 especially interesting by the fact that the smooth shells show in the 

 interior the characters of an Atrypa and not of an athyroid brachiopod, 

 which they strongly resemble externally. Haughton and Etheridge (see 

 farther down) removed the exceedingly closely related Rhynchonella pJioca 

 Salter from Rhynchonella, and placed it with Atrypa simply because 

 they could find no aperture in or under the beak, f have now obtained 

 positive evidence of the near relationship of the Ellesmereland form (as 

 well as of L. phoca from Beechey Island) to Atrypa by getting at the 

 characters of the interior and finding spiral cones with their top directed 

 towards the middle of the dorsal valve. The number of the spiral rings, 

 in one specimen where they are most clearly visible, is eight. In hori- 

 zontal section the cones show an oblong form, with the greater dia- 

 meter in the direction of the length of the shell. The inner side is flatter 

 than the outer, just as in Atrypa reticularis. The two cones also seem 

 to be very close to each other at the base. As to the loop, it is exactly 

 of the same type as in Atrypa, as far as can be seen from the speci- 

 men mentioned above. 



We have here before us what we might call a smooth Atrypa, and 

 as one of the generic characters of a true Atrypa is a rather promment 

 striation or fine plication, we are obliged to put these shells into a new 

 genus. I had myself intended to establish a new genus but learnt at 

 an early date that Dr. W. H. Twenhofel of the University of Kansas, 

 in the manuscript of a monograph on the Ordovician and Silurian 

 rocks and fossils of the Anticosti Island, had preceded me by proposing 

 a new generic name Lissatrypa, for the same type of shells, founded 

 on a small Athyris-Yike biachiopod. He will accordingly stand as the 

 author. 



On first looking over the material and examining the form in question 

 I though that I had the true Lissalrypa phoca^ Salter before me. 



1 1852. Rhynchonella phoca Sai^ter. Appendix to Sntherlands Journal of a Voyage 

 in Baffins Bay and Barrow Strait, p. 226, pi. 5, figs. 1 — 3. 

 18.58. Atrypa phoca Haughton. Journal of Royal Dublin Society, vol. 1, p. 240, 

 pi. 5, figs. 3, 4, 7. — — Continued on next page. 



