136 Olusan Shells. [No. 2, 



to one of the varieties of A. cggneum, that at first sight, it might 

 be difficult to distinguish them ; but on opening the valves, the 

 superior splendour and vivid colouring of the Chinese shell at once 

 suggest a specific difference. A. cygneum shews vestiges of raised 

 rays, similar to the three on the surface of A. gibbum, but in an 

 English specimen, of the variety incrassatum, does not present the 

 concentric rugse on the beaks, which are exhibited by Irish speci- 

 meus of another variety, in which however, they are closer and 

 more delicate than in the Chusan shell. The sub-cardinal muscular 

 impressions are more immediately under the beaks in A. gibbum, 

 while in the British species they are more removed towards the 

 anterior side. 



" Sometimes 5 inches in length. Very common in mud in the 

 canals. Sold in the bazaars as an article of food. Large specimens 

 are very brittle, and precaution should be taken to dry them in the 

 shade." 



TJnio (Thelideema, Swainson,) Leiii, Gray. 



Testa crassa, subovata, alata, compressa, umbonibus dentibusque 

 cardinalibus extremitati anticse angustiori approximatis ; valva sinis- 

 tra dente cardinali interiori margineque cardinali pene parallelis ; ilia 

 versus dentem lateralem mediocriter productam spectante ; valva 

 dextra dente cardinali unica crenata ; valvis intus minime profundis ; 

 margarita iridescente, pallide salmonis colore tincta ; natibus minime 

 promineutibus ; rugis seriebus duabus e linea umbouali divaricatis ; 

 posterioribus simplicibus, anterioribus, basalibusque nodulosis, testam 

 exteriorem munientibus, epidermide flavo-olivacea. Length 2 inches, 

 breadth 3, weight of the two valves If oz. 



The interior lobe of the cardinal tooth in the left valve is in a 

 line with the lateral tooth, or nearly so. The anterior impression 

 of the adductor muscle is finely sculptured in a radiate crystalliform 

 manner. The epidermis is slight yellowish olive, verging into light 

 brown. The posterior margin is sinuous, owing to the ends of the 

 nodulous radiatiug ribs, which diverge in 2 curved series from the 

 nmbonal slope : those towards the posterior margin and wing being 

 simple, while those which run towards the basal and anterior margin, 

 consist of a series of nodules. The two smaller muscular impres- 



