1855.] Chusan Shells. 137 



sions of the cardinal group are in this species situated transversely, 

 one of them being remote from the large impression, but in U. 

 divergens, one is situated above the other, and both adjoin the large 

 impression. 



This shell is evidently the same species as that figured by Gray 

 in Griffith's Cuvier, Vol. XII. PL 21, fig. 1, but without a descrip- 

 tion. The aspect of the shell, and still more that of IT. divergens, 

 reminds the observer of the thick nodulous forms which inhabit 

 the waters of North America, and is quite unlike that of any of 

 our Indian species, only one of which attains any moderate degree 

 of thickness. 



" A perfect specimen of this and a single (left) valve of the next 

 species were found in a house at Tinghae. They are eaten by the 

 inhabitants, who asserted that the shell is found in fresh-water 

 somewhere on the Island. At Macao, Dr. Cantor afterwards saw a 

 specimen with a gentleman who had received it from a native of 

 Canton. The latter asserted that the shell inhabited the mud in the 

 Canton river, at some distance in the interior." 



Unio Theliderma, Sw.) divergens, Benson. 



Testa crassa, angulato-ovata, subalata, tumidiuscula, facie externa 

 tuberculato-plicata, rugis seriebus duobus e linea umbonali divari- 

 cantibus ; posterioribus simplicioribus, anterioribus basalibusque ple- 

 rumque nodulosis ; natibus mediocriter prominentibus, epidermide 

 nigrescente, striis subimbricatis. Valvse sinistra dente cardinali inte- 

 riori versus angulum marginis posterioris basalisque spectante, ad 

 latus exterius laminis pluribus munito ; dente exteriori pene obsoleto 

 brevi, a basi interioris divaricato ; dente laterali brevi crasso. Long. 

 2.65, Lat. 3.5 poll. 



The lateral tooth is nearly parallel with the direction of the inner 

 cardinal tooth, instead of forming, as it were a prolongation of the 

 same line, as in the last species. The anterior impression of the 

 adductor muscle is irregularly reticulate. Anterior margin sinuous, 

 from the protrusion of the extremities of the rug83. Weight of a 

 single valve 2f oz. nearly. It is not very distantly related to the 

 American species IT. costatus, Rafinesque (undalaius, Barnes) figured 

 in Conrad's Monograph in plate No. 17. 



t 2 



