70 ZOOLOGY. 



would lead me to adopt the name given by that author, did it not appear 

 that the work was not published for several years after it was printed. 

 It was not known to the naturalists of this country, France, Germany, or 

 England, until the year 1824." (Say's Am. Conchology.) Swainson uses 

 both names, restricting Schumacher's to the Margaritifera {2)1. 76, jig. 47) 

 of Europe, and Say's to the form A, undulata. 



Stroj>hil2cs, Eafinesque, 1820 (Psetidodon, Gould, 1844, Proceed. Bost. 

 Soc. p. 160, witli four species), has a small swelling instead of regular 

 cardinal teeth, and the soft parts differ in liaving the young, after they leave 

 the ovaries, deposited transversely in the exterior branchipe, instead of being 

 in vertical folds, as in most of the species. In Diplasma of the same 

 author, founded on some shells from Hindostan, there are anterior as well 

 as posterior lamellar teeth, and these are double in the right valve anteriorly, 

 and in the left posteriorly. 



Rafinesque, in the " Continuation" of his Monograph of the Bivalve 

 Shells of the river Ohio, institutes a genus, Loncosilla, for a solenoid shell, 

 brought by Dr. Burrough from the river Jellinghy, in Bengal. Rafinesque 

 considered it to be allied to Anodonta, on account of its fluviatile habits, 

 but the characters of the shell are such as to induce us to coincide with 

 Dr. Burrough in believing it to be essentially a solen. The shell is less 

 than an inch long, " somewhat swelled, both ends rounded, and a little 

 gaping, back horizontal ; outside and inside smooth and whitish." 



Lamarck considered these mollusca to be hermaphrodite ; and the 

 dissections of competent anatomists, such as Neuwyler and Van Beneden, 

 confirm this view. 



Dr. J. P. Kirtland of Cleveland, well known as a successful cultivator of 

 natural science, announced, in the twenty-sixth volume of Silliman's 

 Journal, his ability to distinguish the sexes by the shell alone in this sub- 

 family. It is well known that the shells of many (although not all) species 

 present individuals which are more full at the base posteriorly, and these 

 were assumed to be females, the enlargement of the shell being, as it was 

 thought, required for the gravid branchiae. Some species, as Unio viridis, 

 may be gravid without exhibiting any change of external form. If some 

 individuals remain barren, and others prolific through a course of years, 

 it is possible that the weight of the gravid branchiae may cause the soft 

 parts to descend and bring with them the shell secreting mantle, which may 

 account for the enlargement without recourse to the theory of separate 

 sexes, which are not found in the allied families. But this explanation will 

 hardly account for the second form in Unio velum or U. flexuosus, or for 

 the extraordinary transverse diamater (as in Unio siliquoideus) which is 

 sometimes assumed in addition to the more common posterior enlargement. 



Dr. Kirtland has discovered the presence of a line which he compares to 

 a byssus (Silliman's Jour., 1840, vol. xxxix. p. 166), by which the young of 

 various species of Unio attach, themselves to extraneous objects, a character 

 which indicates an affinity M'ith the Arcidae and Mytilidie, with which they 

 have other afiinities. 



The genus Castalia, from the rivers of South America, is allied to Area 

 274 



