^14, SCIENTIFIC RECORD FOR 1884. 



, ".The Djantle vrhicli covers tbe dome of .tlie Ijiody is tough aud thick; 

 the sides are smooth aud nearly free from papillae. The superior me- 

 dian line is a little depressed. The basal part of the anterior end in 

 life, i^s prolonged beyond the general mass, in a wide trough, with the 

 convexity' upward, and somewhat expanded at its anterior extremity. 

 About one-third of the Ayay from the anterior end, the mantle is perfo- 

 rated by an orifice, which pierces it. in the vicinity of the mouth. The 

 edges of this orifice project from the geueral surface, and it is liued with 

 close-set small papillffi. At about the same distance from the posterior 

 end is another tubular perforation, holding a similar relation to the 

 anus ; whicli has, however, plain edges, and is not internally papillose." 

 When the mantle is open, the small valves become apparent. These 

 are " inclosed in two little sues in the substance of the mantle. The 

 nmboues are near together, apparently connected by a brown gristle, 

 resembling an abortive ligament, and are nearly over the heart. The 

 valves are about ten millimetres long, and one millimetre wide, destitute 

 of epidermis, prismatic or pearly layers. There are no muscular or 

 pallial imi^ressions, no adductors, hinge, or, teeth-" Tliey jcesemble in 

 form tiie exterior of the shell called Gervillia, and have a pure white 

 color. "As they lie in, the body, t)jey,xliy(?j^:ge at a rather wide angle 

 from the beaks, forward. The embryonic valves are retained like two 

 tiny bubbles on the umbones." 



The affinities of this new form are even doubtful. The classification 

 chiefly in vogue for the bivalve moll usks is based upon the number and 

 relations of the adductor muscles of the shell, and Mr. Dall remarks 

 that, if such classification is retained, the new form should be distin- 

 guished as the representative of a distinct order, Avhich might be called 

 '■'■AmyariaP He doubts the propriety of such a separation, however, 

 but very properly claims that it is the type of a new family which he 

 calls Chlamydoconchw, and which would be generally named, with the 

 ordinary family termination, Chlamydoconckidoe. The species is named 

 after its discoverer, Mr. C. E. Orcutt. It is evident, observes Mr. Dall, 

 that " the genus does nothing toward bridging the gap between the 

 gastropods and pelecypods [or bivalve mollusks], but is simply a remark- 

 aj?]ly aberrant form of. the latter group, and probably derived from some 

 form with an external shell. It is able, according to Mr, Orcutt, by 

 sphincter-like contractions of the mantle, to produce currents of water 

 oyer the gills, which, are probably finally ejected by the anal tube." 

 (ScisT^ce,, TY, pp^ 50, 51.) 



^ , . Gastropods. 



The Ojjerenlum of Gastropods. — The development of the operculum of 

 the Gastropods has been studied by F. Houssay on examples of Littorina, 

 Ifnrex, and Purpura. The foot alone is implicated in the formation of 

 the operculum, but "only a small, very clearly defined portion of it." 

 Quite close to the nmrgiu of the operculum w^hich adjoins the columella 

 when the length is restricled, a small transverse fif^sure Avas found which 



