NO. 1 SOOT-RYEN : THE FAMILY MYTILIDAE 77 



American shell described by Philippi (not Modiola opifex (Say) Verrill 

 and Bush, 1900, which is Modiola divaricata (Philippi) ). If the locality 

 for M. opifex is correct, and it must be, this name should be used for the 

 Mediterranean species, with Modiolus sulcatus Risso 1826 (non Lam- 

 arck 1805), Modiolus barbatcllus Cantraine 1835, Modiola petagnae 

 Scacchi 1836, and Modiola costulata Philippi 1836 as synonyms. The 

 Mediterranean species has the same branched hairs on the periostracum 

 as described by Philippi for his Modiola opifex but, until they are proved 

 conspecific, the oldest name, apparently Mytilus chenui Recluz 1842, 

 must be used for the east American species. 



The common west American species has been named Modiola opifex 

 Say or Modiolaria denticulata Dall 1871. What M. denticulata Dall 

 really is, is difficult to tell. After a careful study of the description and 

 comparison with specimens of the common west coast Gregariella, there 

 seems no other solution than to consider Modiolaria denticulata Dall 

 another larger, differently formed species of Gregariella; but only a study 

 of the type can solve the question. Whether the west American species 

 is conspecific with the Atlantic one has not been proved, but they are at 

 least closely related to each other. Therefore chenui Recluz 1842 is used 

 as the specific name. The other more southern species, Crenella coarctata 

 Carpenter, is likewise very close to Modiola divaricata Philippi ^iV/j'/i- 

 lus coralliophagus (Gmelin), from the Atlantic. 



The west American species of Gregariella^ except denticulata, are 

 easily separable. 

 Key to the west American species : 



Sculpture forking along the distinct keel, 



hairs on periostracum smooth coarctata (Carpenter) 



Sculpture consisting of radial lines crossed 



by incremental lines, keel weak, hairs on 



periostracum branched chenui (Recluz) 



Gregariella coarctata (Carpenter) 1856 

 Plate 9, fig. 48 ; text-fig. 64 



Crenella coarctata Carpenter, Catalogue of the Reigen Collection of 



Mazatlan Mollusca, 1856, pp. 123-124. 

 Holotype: British Museum. 

 Type loc: Mazatlan, Mexico (here designated). 



Remarks: Carpenter's description leaves no doubt about this species, 

 which is credited to Dunker in the literature. It is very close to Modiola 

 divaricata Philippi 1847 from the West Indies, which is supposed to be 



