288 AMERICAN JOURNAL 



Albers in the group Rhytida, and as it has no jaw, while the 

 dentition resembles that of Glandiyia^ it belongs to the Testacel- 

 lidiB rather than the Helicidae. The author conjectures that a 

 number of allied species will also have to be removed from the 

 Helicidse, when the soft parts are examined, and Conchological 

 characters are not wanting to distinguish the group. 



On the Spscific Distinctness of Anodonta anatina. By R. M. Lloyd. 



•' There has been a diversity of opinion as to whether Ano- 

 donta anatina is a distinct species or only a variety of ^. cygnea." 



The author has attentively studied these animals and believes 

 them to be distinct species, pointing out diflferences in the soft 

 parts. He states that when the branchial orifice in Unio or 

 Anodonta " from any cause becomes covered by sand or mud and 

 the anal one remains free, it will then draw water in through the 

 anal opening and expel it through the branchial one, causing the 

 sand or mud to be blown away with very great violence, after 

 which the normal state of affairs is resumed. This action is 

 purely mechanical, the animal relaxing the adductor muscles, 

 the valves gape, the opening, however, which would otherwise 

 have been formed remaining closed by the thickened edges of 

 the mantle being kept in contact ; this causes the water to enter 

 the anal orifice ; then the valves are suddenly closed, and the 

 water ejected through the branchial opening, the whole action 

 being, in fact, exactly that of a pair of bellows. If both orifices 

 are covered and there is water between the valves, they are 

 brought together and the branchial one freed, the anal one being 

 afterwards uncovered by the ordinary action of the current." 



No. 29. May, 18V0. 



Morphological Researches on the Mollusca. By M. Lacaze 



DUTHIERS. 



One of the most difficult types of the Mollusca to reduce to a 

 theoretical plan is nndoubtedly that of the Gasteropods. I pro- 

 pose to show that, by taking the relations of the organs and of 

 the nervous system, it is always possible to refer the various 

 forms to a single plan. 



Let us reduce the body of the Gasteropod, for sake of sim- 

 plicity, to four parts — the head, the foot, the visceral mass, and 

 the mantle. If we unroll the body of a species with a turbinated 

 shell we shall have beneath the head and below the foot a re- 

 versed cone containing the viscera. 



The relations of these parts are essentially variable. Thus 

 the head is often separated from the visceral mass by a true 

 neck. As to the mantle its morphology is difficult. 



