ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 735 



is a well-marked Cymbulid which has lost its pseudoconch, and it diflfers 

 from a Gymuosomatous Pterojiod in the following characters : — ^It has a 

 single pair of tentacles ; the cerebral ganglia are on the sides of the 

 oesophagus, and not dorsal or applied one to the other ; the foot has not 

 the characteristic horse-shoe shape, and there is a single hepatic duct. 

 It belongs to the family of the Cymbuliidse, because it has no shell and 

 a deciduous pseudoconch ; the head exhibits a ventral flexure, and the 

 tentacles are symmetrical. 



•y. Gastropoda. 



Gastropoda and Scaphopoda of the West Indian Seas.*— Mr. W. 

 H. Dall has issued the second part of his report on the MoUusca collected 

 in the Gulf of Mexico. A large number of new species are described, 

 and it is found that three families, the Pleurutomida9, Ledidfe, and 

 DentaliidcT, furnish nearly 28 per cent, of the species of the abyssal 

 fauna collected by the ' Blake.' Mr. Dall points out that the most 

 important characteristic of abyssal life is that it, and it alone, exhibits a 

 fauna in which the reciprocal struggle is nearly eliminated from the 

 factors inducing variation and modification. There is no mimicry or 

 sexual selection where all is dark. In the struggle for life of the 

 abyssal animal he is pitted against the physical character of his environ- 

 ment, and not against his neighbour or the rest of the fauna. Hence 

 we should have, and really do have, the process of evolution less obsciu-ed 

 by complications in the abyssal fauna than is possible elsewhere. From 

 a study of these animals in the light of their environment much may be 

 hoped towards the elucidation of great questions in biology, and 

 naturalists should strive to promote deep-sea dredging as essential to 

 the progi-ess of science. The rain of food from the sinking of weak or 

 dead surface forms is unquestionable, and the supply must, in the nature 

 of things as we know them, far exceed the demand. This is illustrated 

 by the absence or disappearance of protective devices in deep-sea species. 

 The genus most abundantly represented of all is Mangilia, which is 

 devoid of an oj)erculum, and the diminution in size and solidity of these 

 protective appliances is marked in all the deep-sea Gastropods. Nearly 

 all the species are carnivorous by hereditary tendency. Those which 

 are not become so by necessity. The ornamentation of the shell in 

 deep-sea Gastropods may be explained in some cases as jn'ovidinc 

 buttresses for the strengthening of the fragile and delicate structures 

 that bear them. Their strength has to be sought for in corrugations of 

 their shell envelope. In the depths where every portion of the shell 

 must be permeated by the surrounding element to equalize the external 

 pressure, and where carbonic acid exerts its usual malign influence on 

 the limy parts of all organisms, we find a protective epidermis developed 

 in most unexpected places. This is the exj^lanation of the fact that in 

 characteristic abyssal animals we find those puzzling and remarkable 

 counterparts of land and fresh-water species of totally diverse groups, 

 which have astonished every student of the Mollusca who has seen 

 them. 



Variations of Cardium edule.f — Mr. W. Bateson has investigated 

 in the Aral Sea and in Egyptian lagoons the variations of Cardium 



* Bull. Mus. Comp. Zool. Camb., xviii. (1SS9) pp. 1-492 (21 p^s.). 

 t Proc. Roy. Soc. Lond., xlvi. (1889) pp. 201-11. 



