Mr. \V. H. Benson on the Ptercypodous Genus Hyalsca. 25 



sculpture, in company with a single specimen of the ordinary 

 form, in 3° S. lat. and 83° E. long. ; and the species again oc- 

 curred to the south of Madagascar. 



The sculpture is variable in respect to the depth of the sulci 

 and of the transverse stricC on the dorsal face. In the Atlantic 

 specimens the ribs are moderately developed, the stria? obsolete, 

 and the white or ferruginous labrum moderately thickened at 

 the edge. In those taken near the Line, in the Indian Ocean, 

 in 1834, the ribs are strongly marked, as well as the transverse 

 striae, and the labrum much thickened, and generally brown. 

 In the minute hyaline variety taken in 1846, the ribs are nearly 

 obsolete, the striae not to be detected, and the lip but slightly 

 thickened and colourless. The single larger variety taken with 

 it has more apparent ribs and a ferruginous labrum ; and when 

 alive, the mouth had a purple tinge, which appeared to be due 

 to the animal. 



Hyalcea lonyirostris, Lesueur. 



When perfectly developed, this species has a bifurcate termi- 

 nation to the labrum, with an emargination between the points, 

 as noted by Souleyet, and the lateral posterior spines run into 

 a long and delicate point. Ranges plate 2 (figs. 7-10) exhibits 

 the shell with these parts in their ordinary truncate form. A 

 small variety, with a blue or violet animal, and a horny-white or 

 hyaline shell, appeared sparingly between 12'^ and 6° N. lat. 

 and 25° and 22° W. long, in the Atlantic, and a larger variety 

 between the Equator and 2° N. lat. and about 90° E. long, in 

 the Indian Ocean. This variety was white and translucent. 



Hyalcea angulata, Soul. 

 Souleyet states that this species offers no differences in the 

 characters of the shell, and that the point of the beak is trun- 

 cate. I have, however, specimens of the ordinary form, and with 

 the anterior vaulted part well developed, in which the beak is 

 thickened at the extremity, and bifid as in H. longirostris. This 

 shell is pellucid, with a brown spot at the place where the narrow 

 rostrum leaves the broad part of the labrum ; and some slight 

 horn-coloured markings are scattered elsewhere. It occurred 

 frequently from 5° N. lat. and 92° E. long., to the head of the 

 Bay of Bengal. Souleyet notes it as rare in the Atlantic, and 

 in the Indian and Chinese Seas. 



Another singular shell, which must be regarded as a distinct 

 species, presented itself in the Atlantic with H. longirostris. 

 It is altogether horn-coloured ; the gibbous portion at the base 

 of the beak, although distinct, is less strongly developed, and 

 not vaulted as in H, angulata ; the bifid rostrum, instead of 



