45 St. Maurice and Claiborne Pelecypoda 45 



De Gregorio seems to have had trouble in identifying any of 

 his material with this species ; in fact it would appear that no 

 specimens of it were contained in his collection. It is by no 

 means rare at Claiborne. It shows a wide range in size and form 

 as our figures will attest. The earlier stages of growth in per- 

 plana appear much like this species ; but as this appears rarely if 

 ever to surpass the size indicated for it by Lea, perpla^ia ma}' well 

 be regarded as a different species. 



This is by all odds the most common species of this genus 

 found in the Claiborne sand bed. Its nearly circular form, 

 thickness of shell for its size and lack of umbonal carination distin- 

 guish it at once from most other forms. 



A thicker, heavier, more rugged and slightly more circular 

 variety of this species is found at Lisbon, Ala., and may be dis- 

 tinguished asvar. Usboncnsis (figs. 16, 17). 



Type. — Phila. Acad. Coll. ; presumably No. 5357. 



Horizons and localities. — St. Maurice: Ruston well, 1200 

 ft. level. La. ; Lisbon, Ala. Claiborne : Claiborne Sands, Ala. ; 

 6 miles W. N. W. of Orangeburg, S. C. 



Specimens figured . — Paleont. Mus. Cornell Univ. 



Trinacria cossmanni Dall, PI. 20. Figs, i, 2. 



Limopsis perplana Cossmann, Notes Compl. &c., 1893, p. 16, pi. i, 



figs. 20-21. 

 Z,7wc/>.s/.? t055wa;/«/ Dall, Trans. Wag. &c.. Ill, '95, p. 605. 



This regularly formed little species is not perplana, SlS Dall 

 has pointed out, but its relationship to the latter is not very dis- 

 tant. For were it not for the somewhat stronger dentition in el- 

 lipsis (or even the j^oung oi perplana) it would be very difficult 

 to separate forms of these species that happen to have about the 

 .same outline. In fact we have been at first in doubt as to whether 

 certain specimens should be placed with cossmanni or ellipsis. 

 Typical cossmanni represents the limiting species of this genus as 

 far as bilateral symmetry is concerned. We do not place it with 

 Limopsis, although with the general straightne.ss of beak there is 

 a tendency to show some ligamental area behind the beak. On 



