Paleontology Zorritos Formation' 133 



an under surface with concentric sculpture similar to that 

 of the outer layer and, in addition, very fine radial lines. 

 Areas imperfectly known, but do not appear prominent. 

 Inner shell unknown. Length. 27.5 ; height. 27.5 ; diameter, 

 13.5 mm. 



This species is very close to P. gliDiiindiis Woodring,^*^ 

 from the Bowden beds of Jamaica, and examination of 

 more material may show the advisability of expressing a 

 relationship closer than that suggested, but such evidence as 

 is now available indicates sufficiently strongly the possibility 

 of specific diflFerence to suggest the naming of the fonn as a 

 new species. Specimens of P. glumindiis have the ventral 

 margin less deeply arcuate, and the umbones less promin- 

 ent, with no radial lines on the under surface of the shell. 

 One fragment of the Zorritos form suggests the possibility 

 of a ventral margin similar to that of glu)ni)idus. but the 

 type here described seems to predominate, and the other 

 differences appear constant. The sculpture of glumindns 

 is coarser and more irregular than that visible on patches of 

 the epidermis of insleyi . 



Two east coast Pliocene species are similar. Phacoides 

 foreuiani Conrad,^*^ from the Miocene of Maryland, differs 

 in having a posterior sulcus and rougher sculpture ; it is 

 identical in shape. P. anodonta Say.^** also from the Mary- 

 land Miocene, attains a larger size than that known for 

 iu^leyi, but adolescent forms of anodonta are similar excep- 

 ting their slightly more orbicular shape, ruder sculpture, 

 and posterior sulcus. The epidermis of aiwdonta is propor- 

 tionally thicker, and the radial sculpture beneath it is much 

 coarser and stronger than in insleyi. 



Two species from the Eocene of California appear to be 



'^Dissertation. Johns Hopkins Univ. 



"'Foss. Med. Tert.. p. 71. pi. 40, tig. 4. 1845 (as Lucina fore- 

 mani) . 



'"Md. Geol. Surv.. Miocene, p. ^^j. pi. 90. figs. 3. 4. 1904. 



