_ 308 - 



angular an'''' sorrir- ' ■' -'" t ■--■■- '--■•>- thai, ^jix tlie rest; '■-■^-""'^-: - 

 more pustular and less regiilar t?ian in S. aroinel la . T'enc;th 

 50, hei,o:bt 48, '"liameter alDont 40 rm, exclii.sive '^f tl"ie spines." 



"Sh" o t;-'t.-ul._o '.;. cii oomparei is seen ' ^•■f-"/: 3t. from 



the t;rpe of the geniis with which it was confused by " " is 



reallj" more like the Pacific er^eci , Q, californica DallJ '-'hich 

 has nearly as many ^lju ;j-.'' ' ^ -• . ._ ^ ,. .. 



ii.; ' ule and long, cylindrical spines." 



■'All species have occasional individuals which have the 



spines and even the rihs nearly ohsolete. Guppy's "'^''■^ian speci- 

 men, and a valve collected in the Pliocene o:^ ., Jost? Tiica, 

 hy Oahh, are of this character, hixt as it is more an individu.al 

 mutation than -j. urue variety I shall not ap :;1„ an„ iistixictive 

 name ' t o i t . " ( D^jU , 1 9 O5 ) . 



Type locality .- Bor:den, Jamaica. 



Shell larre, .:iai;aive, equivalve, decidecf" ilafceral, 



outline subquadrate ; dorss" in scarcely curved, rou.-d.ino- into 



the fently curved "posterior margin, ''.'hi eh passes m.ore abruptly 

 into the truncate:' base; anterior marjin oolique across the 1" "''■ ' 

 insinuated tt the base of '' " le and then abruptly flexe(! 

 ou-t7;ard; umbones anterior in -vosition, m.oc'erately inflated ai-id 

 modera'^ely high; lunule large, deeply impressed, its \ " ' ' ' ^"'- 

 tlon raised toward the margin; e temal sitrface soiilptured with 



