78 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



identical with Mytilus coralliophagus Gmelin, based on PL 84, fig. 752, 

 of Chemnitz. The radial sculpture on the posterior part is divaricating 

 along the keel, the anterior radial sculpture is very distinct, the umbones 

 anterior, and the hairs on the periostracum on the keel are fine and dense 

 without branches. 



Occurrence: Carpenter says that this species is found burrowing in the 

 shells of Spondylus calcifer and Murex regius. Depth records are from 

 2 to 9 fms. The Hancock material extends the distribution considerably. 

 Distribution: Laguna de Scammon, Baja California, to Isla Taboga, 

 Panama ; the Galapagos Islands. 



Gregariella chenui (Recluz) 1842 

 Plate 8, fig. 40; text-fig. 65 



Mytilus chenui Recluz, Revue Zool., vol. 5, 1842, p. 306. 

 Syn.: Modiola opifex auct. non Say 1825. 



Botulina denticulata auct. non Dall 1871. 

 Holotype: ? 

 Type loc: Brazil. 



Remarks: Shell white, small, with the umbones anteriorly placed, of a 

 broadly oval form with sloping curved anterior and posterior margins, 

 broadest in the posterior half. Periostracum yellowish with long branched 

 hairs on the posterior part. Sculpture consisting of a few radial anterior 

 striae, a median part without radial sculpture, and distinct radial striae 

 on the posterior part, the first not reaching to the ventral margin, the 

 dorsal ones bent backward. The radiating striae crossed by distinct but 

 somewhat irregular concentric lines, giving the posterior part a decus- 

 sated sculpture. The anterior dorsal margin somewhat thickened and 

 crenulated ; the posterior dorsal margin with strong crenulations which 

 become smaller on the posterior margin and hinder part of the ventral 

 margin; the middle part of the ventral margin smooth. The ligament 

 internal and descending backward, supported by a distinct nymphae. 



As stated earlier, the west American species seems to be identical with 

 the east American one described and figured by Philippi (1847) as 

 f Modiola opifex Say. There might be some uncertainty as to the oldest 

 name for this species. If Modiola opifex Say, or the Mediterranean 

 species, should turn out to be the same as the species from Brazil, which 

 is very improbable as the sculpture is different, then M. opifex Say 

 could be used for the west American species too. Until they are proved 

 conspecific, the name chenui Recluz seems to be the oldest one available. 

 Occurrence: The Hancock collections contain many samples of dead 



