614 SCIENTIFIC RECORD FOR 1884. 



"The mantle which covers the dome of the body is tough and thick; 

 the sides are smooth and nearly free from papillje. The superior me- 

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

 life is 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 way from the anterior end, the mantle is perfo- 

 rated by an orifice, which ]>ierces it in the vicinity of the mouth. The 

 edges of this orifice project from the general surface, and it is lined with 

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

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

 anus ; which 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 sacs in the substance of the mantle. The 

 umbones 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 i^early layers. There are no muscular or 

 pallial impressions, no adductors, hinge, or teeth." They resemble in 

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

 color. "As they lie in the body, they diverge 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 vogne for the bivalve mollusks is based upon the number and 

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

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

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

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

 but very properly claims that it is the tyi)e of a new family which he 

 calls Chlamydocojichce, and which would be geiierally named, with the 

 ordinary family termiwation, ChlamydoconcliMoe. The species is named 

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

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

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

 ably 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 

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

 {Science^ IV, pp. 50, 51.) 



Qastropods. 



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

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

 Murex, 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 margin of the operculum which adjoins the columella 

 when the length is restricted, a small transverse fissure was found which 



