LITTORINA. Panama Shells. 171 



that the former are the extreme limits of variation rather than 

 distinct types. 



Station. We found this species on ledges and large fragments 

 of rocks at or above high water mark. 



Habitat. Sitcha, Mexico, and San Salvador ; Philippi. 

 San Salvador ; Jay. 

 Taboga, and Panama ; C. B. A. ! 



We collected 2400 specimens. Dr. Philippi's statement of 

 habitat is " Oceanus Pacificus, American! borealem alluens ; 

 Sitcha ; ora Eeipublicse Mexico ; S. Salvador in America 

 centrali :" Philippi. It is scarcely credible that this species 

 should have been found in so high a latitude as Sitcha. No 

 original testimony is cited. 



Littorina aspera, var.. is more slender, and the sculpture is 

 reduced to spiral impressed lines. 33 specimens were collected 

 at Panama. 



233. Littorina atrata. Nov. sp. 



Shell conic when young, subglobular when mature : black, 

 sometimes with a few whitish spots on the last whorl : with 

 spiral keels varying in size and number ; usually a strong 

 sharp keel is seen on the periphery of the last whorl and in the 

 suture, and another appears on the upper part of the whorls, 

 with one slightly developed between them ; with two or three 

 well developed keels beneath the periphery of the last whorl : 

 apex acute : spire small, eroded in full grown shells, with the 

 outlines moderately curvilinear : whorls four, a little convex, 

 with a well impressed suture ; last whorl with an acute 

 periphery in the young, rounded in the mature shell : aperture 

 broadly ovate : labrum well excurved : umbilicus very small. 

 This species is variable in form and in sculpture. 



Mean divergence from 65 to 90 in different stages of 

 growth ; length .08 inch ; breadth .06 inch. 



Station. In or near cavities of rocks between half tide and 

 high water levels. 



