44 



ALLAN HANCOCK PACIFIC EXPEDITIONS 



VOL. 20 



multiformis (Carpenter) 



very difficult to place and I must admit that now and then some charac- 

 ters are more like Hor?nomya than Brachidontes. Perhaps there still 

 might be unrecognized species of this genus, too. 

 Key to the west American species: 



1. Sculpture obsolete on the ventral side, 

 sometimes the whole surface nearly 

 smooth, the length usually less than 

 12 mm 



Sculpture more uniform, also on the 

 ventral side 



2. Coarsely ribbed species of variable out- 

 line, purplish with heavy black perios- 

 tracum, and a series of small teeth 

 Sculpture finer, periostracum lighter, 

 outline more constant, some of the teeth 

 larger than the crenulations 



3. Umbonal keel flat, shell not inflated, 

 sculpture uniform over all the shell, ribs 

 fine and close-set, shells stained yellow- 

 ish-brown, anterior margin broadly 

 rounded 



purpuratus (Lamarck) 



Umbonal keel usually distinct and shell 



inflated, sculpture obsolete or weaker on 



the ventral side, anterior margin narrow 



4. Larger species to 17 mm of regular form 



Smaller species to 10 mm of irregular 

 form 



playasensis (Pilsbry 

 and Olsson) 



puntarenensis (Pilsbry 

 and Lowe) 



houstonius Bartsch and 

 Rehder 



Brachidontes multifonnis (Carpenter) 1855 



Plate 3, fig. 13; text-fig. 28 



Mytilus multiformis Carpenter, Catalogue of the Reigen Collection of 



Mazatlan Mollusca, 1855, pp. 118-120. 

 Syn.: fModiola semilaevis Menke 1849. 

 Holotype: British Museum. 

 Type loc: Mazatlan, Mexico. 



Remarks: Carpenter's description seems to have been based on what here 

 is considered to be the true multiformis and on small heavily sculptured 



