MUSEUM OF COMPARATIVE ZOOLOGY. 299 



posteriorly directed groove or fossette ; surface smooth or concentrically sculp- 

 tured. Type Necera adunca Gould. 



This is equivalent to Smith's Section F. It would include, according to his 

 description, Neara Brazieri Smith. I have compared specimens of N. adunca 

 Gould, received from Drs. Arthur Adams ^d Gould, which agree perfectly with 

 Adams's description of Leiomya. The cardinal tooth in the right valve is bifid 

 at the tip and very small ; hence Adams in his diagnosis ascribed two cardinal 

 teeth to this valve, but I think they should be counted as one. 



What the shell is, described by my friend Smith as type of his Section J, 

 under the name of Necera adunca Gould, I do not know. He has evidently 

 been misled by a wrongly named shell. It is certainly an entirely different 

 species and section from Leiomya. It has no cardinal teeth, a small central 

 fossette, a small thickish anterior and posterior lateral in the right valve, and 

 a similar anterior lateral (only) in the left valve; the surface is finely ridged. 

 It appears to be the only species with these characters, and I would sug- 

 gest the name of Vulcanomya Smithii for it in default of any other legitimate 

 designation. Its external characters and size closely resemble those of the 

 genuine N. adunca Gld., which would account for the error, in the absence 

 of types. 



Mr. Smith kindly informs me that he has re-examined the specimens, and 

 finds nothing to change in his description of them. They were received at the 

 British Museum with Gould's name attached by some one unknown. 



Section PLECTODON Carpenteb. 



Plectodon Carpenter (Suppl. Rep. Brit. As., p. 638, Aug. 1864) is closely re- 

 lated to Leiormja. It diifers in the insertion of the cartilage behind and under 

 the beaks, instead of on the hinge- margin or in a fossette; in having, rather than 

 a true tooth upon the margin, a tooth-like prominence formed by the spiral 

 twisting under the beaks of the hinge-margin itself, upon and over which, in 

 P. scahcT, there is a minute external ligament; lastly, in Plectodon there is a 

 granulated surface much as in Poromya. The pallial sinus appears to be about 

 the same in both, and the tips of ^he siphons are protected, in both groups, 

 as in Schizothcerus, by a leathery ring, flattened and broadened at the sides. 

 Until recently only two right valves of Plectodon were known, but in 1873 I 

 dredged at Catalina Island, California, in 16 fms., mud, some half a dozen 

 living specimens, which have enabled me to make a careful comparison with 

 my Necera granulata. There can be no doubt of their generic identity, and 

 even considered as species they are very similar, the intwisting of the margin 

 being less marked in granulata and the supposed external ligament obsolete. 

 I regard Plectodon, therefore, as a mere section of Leiomya, which might also 

 include Rhinoclama, which is of about equal value with Plectodon. 



