96 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



Remarks: Two small broken specimens from Manta, Ecuador, seem to 

 be referable to Hanley's species, which has not been recorded since it 

 was described. The specimens have a length of 11 mm, including the 

 incrustation, which protrudes beyond the posterior margin for about 1.5 

 mm ; on the right valve only in one of the specimens and on the left in 

 the other, apparently indicating only the young age. The incrustation is 

 found as two parallel thicker ridges separated by a radiating groove with 

 more irregular sculpture. The anterior and ventral parts are covered 

 with a thin granular incrustation. This species may perhaps be placed in 

 subgenus Labis, but is retained in Diberus until more material is ob- 

 tained. Tomlin (1928) has listed Lithophaga appendiculata (Philippi) 

 {=bisulcata Orbigny, a West Indian species), from Isla Coiba, Bahia 

 de Panama, but perhaps his specimens may be referred to Lithophaga 

 (Diberus) canalifera also. 

 Occurrence: 1 to 12 fms, sand. 

 Distribution: Panama?; Ecuador; South America. 



Lithophaga (Diberus) plumula (Hanley) 1843 

 Plate 10, fig. 55 



Modiola plumula Hanley, Catalogue of Recent Bivalve Shells, 1843, 



p. 239. 

 Syn.: Lithophagus calyculatus Hertlein and Strong 1946. 

 Holotype: British Museum. 

 Type loc: Panama, in Spondyli. 



Remarks: Carpenter (1857) admits two varieties or forms, a slender 

 one, gracilior, and a shorter one, tumidior. The featherlike incrustation 

 and the muscle scars are typical in both forms. The periostracum gener- 

 ally forms transverse wrinkles on the dorsal side. The largest specimen 

 has a length of 55.8 mm including the projection of the incrustation, or 

 46 mm without ; but ordinarily the specimens are 20 mm to 30 mm long. 

 The anterior retractor leaves a narrow but very elongated scar com- 

 mencing just behind the umbo. 



Occurrence: The larger part of the specimens were collected in shallow 

 water with corals, some were taken on or in rocks or sand, and a few 

 were found in depths from 14 to 20 fms, where the bottom was stated 

 to consist of sand and shells. All stations were within the known range 

 of distribution, except for the one from Isla Espanola (Hood Island), 

 Galapagos Islands, where the large specimen, total length 50 mm, was 

 taken. It seems to have been unknown from these islands before. 

 Distribution: Gulf of California to Peru. 



