CAVOLINIIDAE 275 



tudinal ribs on the upper valve are almost effaced and the lateral points which form its 

 greatest width are placed towards the centre, whereas in the other species of Cavolinia 

 they are nearer the posterior end. The upper lip, when viewed from above, projects 

 forward about as much as that of C. longirostris , but curves slightly upwards instead of 

 over the lip. It is also rounder laterally and the edge is serrated. The posterior " thorn" 

 curves upwards over the dorsal side. The lower side is not nearly so globular as in other 

 members of the genus and the lip is developed rather strongly. The specimens from 

 stations 80 and 89 measured 6-7 mm. in length. 



Distribution. In all seas between about 40° N and about 40° S latitude. Excep- 

 tionally it wanders with a warm current as far as 50° N (Massy, 1909). 



Cavolinia tridentata (Forskal), 1775. 



Anomia tridentata, Forskal, 1775. 

 Hyalaea affinis, d'Orb., 1826-33. 



St. 78. Young-fish trawl, 1000 (-0) m. : i specimen. 

 St. 85. 4-5 m. net, 2000 (-0) m. : i specimen. 

 St. 86. 4-5 m. net, 1000 (-0) m. : 13 specimens. 

 St. 89. Young-fish trawl, 1000 (-0) m. : i specimen. 

 St. 244. I m. net, horizontal, 55 m. : 4 specimens. 

 St. 288. Young-fish trawl, 250 (-0) m. : i specimen. 

 St. 289. Young-fish trawl, 125-225 (-0) m. : i specimen. 

 St. 294. I m. net, horizontal, 55 m. : 4 specimens. 



Six of the above hauls were made off the African coast from the Gulf of Guinea to 

 the Cape. The remaining two were west of Tristan da Cunha. This comparatively large 

 species occurs in all warm seas. The specimen from St. 85 had a shell measuring 15 mm. 

 in length and appeared to be a form between the type and var. truncata, Boas. This 

 variety "se montre dans la partie la plus meridionale de I'Atlantique et la partie occi- 

 dentale de I'Ocean Indien" (Boas, 1886, p. 212). The same author {loc. cit., p. 211) 

 mentions that examples of this species in the Eastern Pacific are smaller (9-13 mm.). 



The specimens from St. 294 possessed fins of a greenish hue. 



Cavolinia uncinata (Rang), in d'Orb., 1836. 



Hyalaea uncinata, Rang, 1836. 

 Hyalaea iincinatijormis, Pfeffer, 1880. 



St. 273. Young-fish trawl, 200-230 (-0) m. : 3 specimens and i shell. 



St. 276. Young-fish trawl, 150 (-0) m. : 5 specimens. 



St. 279. 4 mm. mesh net on trawl, 58-67 m. : 8 shells. 



St. 288. Young-fish trawl, 250 (-0) m. : 1 1 specimens ; i m. tow-net, oblique, 73-0 m. : 2 specimens. 



The above, which measured 6-7 mm. in length, were all caught off the Gulf of 

 Guinea and the Congo river. The species is generally distributed in tropical and sub- 

 tropical waters. Boas (1886, p. 120) mentions having seen a specimen of 11 mm,, but 

 states that the usual size is 7 mm. The most closely allied species is C. tridentata 

 (Forsk.), from which it is easily distinguished by the lateral points of the shell being 



