o r70 



diam. , 9 mm. ; lenp'th of hir.p-e, 12 mrn. 



Remarks .- A fraginent of an apparently mature left valve, tv/o 

 immature right valves a.j ^ ounger left constitute the reoresent- 



ation of this sharply-defined species, ■^'he fragment presents only 

 the n.-i:bonal and posterior dorsal portion of the shell and therefore 

 some uncertainty attenr^s its position; "but in so far as can he de- 

 termined, the outline, sculpture and a^^ricles testify to its place 

 in this species. The left valve is decidedly pecteniform sin:.'e it 

 is only moderately and uniformly inflated, while the right valve 

 is strongly inflated in the umhonal region. In sculpture the two 

 valves are notably different. 



_S. cookii is recognized by its suborbicular outline, prominent 

 auricles, strongly inflate'^ riprht valve, sciil-otured v;ith spinose, 

 broad primary radials and finely scabrous, longitudinally striated 

 secondaries, and moderately inflated left valve v.dth more equally 

 developed -nrimaries and secondaries. 3_. bostrychites is less inflat- 

 ed, less orbicular, more inequilateral, less auriculate, \"i'"h less 

 pronounced sculpture, the ribs being much smaller and t;:e spines 

 shorter. 



This species is named fo' Dr. 0. v7ythe Jooke, " '■".e 'J. 3. 

 Geological '"urvey, "ho is making valuable contributions to the 

 Tertiary molluscan "oaleontolor-y of the './est In'-lios. 



Occurrence .- laver J.-iocene : "Bo-.vden, beds, Eov/den, Jamaica. 



