- 16;^ - 



ized Tdj' the imique posterior keel, which, though Slip-ht, is note- 

 worthy, and the ooncomitant oblique truncation of tl .'-ero-lat- 

 eral margin. Inmature forms do not display these features, "biit 

 they may readily he distinguished froi:i the young of the other spec- 

 ies by. ISieir erteir^al sculpture. Oompared \7ith adults, the primary 

 radials of young shells are prominent and the secondaries sunrress- 

 ed, 



Guppy referred this form to £. pennaoea (Laraarck) or G, de- 



-A- cui'satus f Linnaeus), hut it obviously differs from the recent, 



which has been given either of those names, being raore conve" , v-lth 



fa. more irreg^alar conton.s and weaker concentric sculpture. Most 

 of Gabb ' s Santo Domin~ian pennaoea are neither that s-oeciss or 

 jamaioensis ; "Siey differ from the latter by being less inflated, 

 more elongated transversely, without the posterior keel and trun- 

 cation, the posterior -argln being rounde' more corfvexly than the 

 anterior, with the pri-^ary radials slightly more prominent. In 

 addition to this form, typical speciirens of jamaicensis are present. 

 G. carbasina Bro^'ai and Pilsbry (l) of the Gatun faixna, is smalley, 



(1). Proc. Acad. ITat. 3ci., Philadelphia, vol. 55, pp. 563-564, 

 pi. S8, fig. 9, 1911. 



vathout the posterior keel and truncatio;., with lov.'er, bro- der vm- 

 bones, more prominent primary radials, more conspicuous concentric 



