l-< H\M. IN | 



I. . OOPEBJ ( larpenter, n. >p. I'l. _';, figg. -j; 



shell oval an.l elevated, wiili angular dona! i 

 side-slopes, Sculpture like Lmerientii. ( 'oh.r <,li\ae ,,n.~, or dull 



earthy In-own, indistinctly clouded IM..IV or ten \\iili liirht blue, 



especially upon the side areas. The lateral areas arc iai-<d, and 



hear irregular nws >f rounded pustules, the young bavin- four : 

 the adull (I to ' s . A >troiig lens reveals a line, suholob-te irranula- 

 tion of the nearly Hat surface between the pustules. The central 

 areas have a line hut distinct and even radial striation, over whieh 

 run acute narrow raised threads parallel to the dur.-al rid-c; upon 

 the ridge these threads are seen to be more or le.-s divei-ifim:, 

 specially ii])on the second valve. The end valves are radially 

 ridged, the ridges bearing elongated pustules, or showing - 

 where such pustules have been. Mucro low, flat. 



Interior bluish, the valves marked under their innbnnes with dark 

 olive. Head valve having 11, central valves 1, tail valve 11 >lits ; 

 teeth roughened but rather sharp; eaves wide, dark, minutely 

 punctulate, but solid, not spongy. 



( iirdle compactly covered with small imbricating, deeply striated 

 scales (fig. 28). Length 40, breadth 24 mill. 



Xmt.tti ('rn: and Bolinas, California. 



This species closely resembles 7. mertei>*ii in shape and sculpture, 

 but it differs entirely in the smaller, distinctly striated or grooved 

 scales, in the sombre coloring both outside and within, in the closer 

 pectination of the inter-liral spaces of the central areas, and in the 

 more developed microscopic granulation of the lateral areas. It 

 cannot be claimed that all or any one of these characters is invari- 

 able, but the balance of them taken together, seem to indicate that 

 differentiation has proceeded to a stage we may call specific. The 

 following species is allied to this in coloring, but differs sufficiently 

 in sculpture, a< well as in the girdle-seal'-. 



The details of sculpture and the scales of all three >p 

 drawn to the same scale. The third valve of/, cooperi is >h..\vn in 

 tb-s. I'D, :](). It must be remembered that the valves behind this, and 

 usually even the third, have less markedly divergent -culpture than 

 the typical form here shown. 



The specimens herein described and figured are from Bolinas, 

 north of San IVanci-co, and since no diagnosis has been published 

 hitherto, thc.-c will be considered the typical specimen-. Carpel 

 specimens were 1 from Sta. Crux. 



