REPORT ON THE MOLLUSCA. 13 



Amusium. 



10. Amusium lucidum, JeflFreys. Station 78 ; 1000 fathoms. 



11. Amusium meridionale, Smith. Stations 146, 158 and 302; 1375, 1800 and 



1450 fathoms respectively. 



These forms have no pigmented ocelli. It must he noticed that they live at much 

 greater depths than the above-mentioned Pecten ; the difference can therefore be easily 

 explained. 



The absence of pigmented ocelli confirms the observation made by Dall about 

 Amusium dalli, Smith.' Dall affirms, however, that this form has only a single gill 

 on each side ; the species which I have examined have two branchial plates of recurrent 

 filaments similar to those of Pecten. 



I have examined a certain number of Pelecypoda, which presented nothing 

 remarkable, and have therefore led to only negative results. Such are — 



12. Myrina coppingeri, 8mit\\. Station 184 ; 1400 fathoms. 



The arrangement and form of the gills exactly resemble those of the allied littoral 

 forms (Mytilidse) already known. 



13. Venus mesodesma, Quoy and Gaimard. Station 135e; 1000 fathoms. 



The gills are normal, and the labial palps very small, as in the littoral species of 

 the same genus. 



LUCINACEA. 



14. Cryptodon moseleyi. Smith. Station 133 ; 1900 fathoms. 



The mantle is quite open ventrally, as in the other Lucinacea. The margin of the 

 two lobes (circumpallial muscle) is very thick in its anterior portion, and the interior 

 surface of this margin is tuberculated and papillary. This is probably what Semper ^ 

 has called "mantle-gills" (PI. II. fig. i,j). 



As in Lucina, the anterior adductor muscle does not come into contact with the 

 circumpallial muscle, but is separate from it, and is carried back to some distance 

 inwards (PI. II. fig. 3, I). 



The two lobes of the mantle are only united at a single point (r), and consequently 

 only form one pallial (anal) aperture, as in Ungulina, instead of two, as in Lucina. 

 This aperture (k) is absolutely sessile, and does not form a siphon, properly so called. 



The foot (d), even taking the rather feeble contraction into account, is short, and 



1 Report on the MoUusca, Bull. Mtis. Comp. Zocil., vol. xii. p. 210. 



2 Die naturlicbe Existeiizbedingungen der Thiereu, Bd. i. p. 208, fig. 48, (i; Aninjal Life, pp. 1G9, 170. 



