80 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



probably the northern west coast species, and the more southern species 

 can, as far as I am able to decide, not be separated from the Caribbean 

 species described by Orbigny as Nuculocardia divaricata. In the area 

 where these two species overlap in their distribution, the southern species 

 seems to be much more like the northern and not typical. The separation 

 of these species is therefore sometimes very difficult without large series 

 for comparison, and a thorough revision is highly needed for Crenella, 

 as for so many other mytilid genera. 

 Key to the west American species : 



Sculpture fine, with narrow interspaces, nar- 



ower than the ribs, which on the central part 



bifurcates in an arrowlike manner; inflated, 



elongate when full-grown, hinge strong, color 



white divaricata (Orbigny) 



Sculpture coarse with interspaces as wide as 



or wider than the ribs, less inflated, more 



rounded form even when full-grown ; hinge 



weaker; color more grayish-yellow decussata (Montagu) 



Crenella divaricata (Orbigny) 1853 

 Plate 8, figs. 42, 44 



Nuculocardia divaricata Orbigny, Hist. Phys., Pol. et Nat. de I'ile de 



Cuba. Mollusques, vol. 2, 1853, p. 311, PI. 27, figs. 56-59. 

 Syn.: Crenella inftata Carpenter 1864. 



Crenella ecuadoriana Pilsbry and Olsson 1941. 

 Holotype: ? 

 Type loc: Cuba. 



Remarks: Specimens from the Caribbean are impossible to separate from 

 specimens from of? Central America, which therefore must be considered 

 to belong to the same species. Crenella inflata Carpenter 1864 seems to 

 be based on specimens of C. divaricata (Orbigny) with a strong hinge; 

 and Crenella ecuadoriana Pilsbry and Olsson 1941 represents, as far as 

 I can decide, an elongate specimen of C. divaricata (Orbigny). One 

 character, which usually is easily seen and which separates C. divaricata 

 from C. decussata, is the peculiar way the ribs on the central part of the 

 disc branch, one set within the other, with the points toward the umbones. 

 Valves which must be referred to C. divaricata are found along the 

 coasts of Baja California north to San Miguel Island, California, some- 

 times together with valves of C. decussata. I am unable to decide whether 

 C. divaricata lives so far to the north, as the few living specimens in the 

 material are all C. decussata. 



