76 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



Length, 13 mm. There are no specimens in the Hancock collections. 

 Occurrence: Moderate depths, the bottom in the type locality consisting 

 of gravel. 

 Distribution: Nunivak Island to Monterey, California. 



Genus GREGARIELLA Monterosato 1884 



Gregariella Monterosato, Nomenclatura Generica e Specifica de alcune 



Conchiglie Mediterranee, 1884, p. 11. 

 Syn.: Botulina Dall 1889. 



Trichomus cuius Iredale 1924. 

 Tibialectus Iredale 1939. 

 Type of ffenus: Modiolus sulcatus Kisso 1826 (non Lamarck 1805, 1819) 



= Modiolus barbatellus Cantraine 1835 = Modiola opifex Say 1825 



(subsequent designation by Crosse 1885). 

 Remarks: There seems to be no difference between Botulina Dall, Tri- 

 chomusculus Iredale, Tibialectus Iredale, and Gregariella, and the first 

 three mentioned genera are considered to be synonyms. The original diag- 

 nosis in Italian says that one third of the valve is smooth, two thirds 

 decussate, the periostracum hairy; the hinge with rudimentary oblique 

 teeth, and the dorsal margin crenulated. The sculpture of Gregariella 

 is slightly unlike that of Musculus, as the first posterior radiating striae 

 are not continued to the ventral margin but stop gradually on the middle 

 part. The mantle margin is smooth, the posterior part forming a branchial 

 siphon open ventrally and an elongate anal siphon. The anterior retractor 

 is before the umbo. 



Dall (1889) introduced the name Botulina as a section of Modiola, 

 without a description, and gave Modiola opifex Say as the only species. 

 (Say described this species in 1825 from specimens found embedded in 

 sand on the valve of a Pecten, which he named nodosus Linne, though 

 he said that the shells, which were presented to the Academy of Natural 

 Sciences in Philadelphia by the U. S. Navy, came from the Island of 

 Minorca. One should suppose that the reference to this locality is more 

 reliable than a species name, and the P. nodosus of Say might be a Pecten 

 maximus Linne.) Modiola opifex Say is also mentioned by Hanley 

 (1842-56, p. 239) as from Minorca. Philippi ( 1847) gave a new descrip- 

 tion of fModiola opifex Say, with a good figure, from a specimen ob- 

 tained in Brazil by Kroyer. Philippi was not sure that his species with 

 long, branched hairs on the posterior keel was the same as Say's, because 

 Say did not mention this distinct and characteristic periostracum. The 

 specific name opifex Say has nevertheless been used since for the east 



