210 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 20 



The number of ribs varies between 36 and 38, and the ribs of the 

 left valve are broader than those on the right. The umbones are stained 

 uath bluish-black. The mantle margin has a heavily pigmented narrow 

 band on the side that touches the shell, but no distinct eye-spots can be 

 observed. The byssus was found intact in two of the specimens and con- 

 sists of thin threads. Heath (1941, p. 305) did not find any sign of a 

 byssus in Lunarca ovalis {^uxg\x\hrt)^pexata (Say), the Atlantic coast 

 species. The abdominal sense organs of L. vespertina resemble those of 

 this species. The labial palps are comparatively smaller in L. ovalis. It 

 may be noted, however, that the specimens examined by Heath had a 

 length of 52 mm. The largest specimen of L. vespertina in the present 

 material measures 17.2 mm in length, 12.8 mm in height, and 9.6 mm in 

 diameter. It is from off Punta Pequena, Baja California (617-37). 

 Occurrence: One of the samples was collected in shallow water, while 

 the other two were both dredged from 24 fms, in sand and sandy mud 

 respectively. Hertlein and Strong (1943) report it from 7 to 13 fms 

 with sand, mangrove leaves. 



Distribution: Off Punta Pequena, west coast of Baja California, Isla 

 Espiritu Santo, Gulf of California (the present material), Mazatlan, 

 Mexico, Corinto, Nicaragua (Hertlein and Strong, 1943). Dall and 

 Ochsner (1928) report it with a question mark as fossil from the 

 Galapagos Islands. This identification, however, is in error (Reinhart, 

 1943). 



Lunarca sp. 



PI. 15, figs. 25 a-b, 26 



Remarks: As mentioned before, three samples are here referred to 

 Lunarca sp. One from the Galapagos Islands consists of a worn right 

 valve which measures 45.7 mm in length, 35.6 mm in height, and 14.8 

 mm in semidiameter, and possesses 35 ribs. The other Galapagos valve 

 (left) measures 43.6 mm in length, 33.2 mm in height, and 15 mm in 

 semidiameter; and has 36 ribs. Another sample is from Panama and 

 consists of a complete specimen which measures 52 mm in length. 41.3 

 mm in height, and 35.5 mm in diameter. The specimen is thick, with 

 swollen umbones, and has 36 ribs. The left valve overlaps the right 

 except anterodorsally and posterodorsally. 



Subfamily Noetiinae Stewart 1930 



Remarks: Stewart (1930) placed this subfamily in the family Glycy- 

 meridae. MacNeil (1938) raised it to family rank under the super- 

 family Glycymeracea. To Noetiidae he referred the subfamilies Stri- 



