72 ZOOLOGY 01 THE VOYAGE OE H.M.S. SAMAKANG. 



5. Terebkatdxa abyssicola. PI. XXI. Fig. 5. Ter. testa trigono-ovali, pellucido-carneola, lsevius- 

 cula, radiatim planicostata et striata, costis striisque fere obsoletis, valvis fere squaliter convexis, medio 

 leviter sinuato-sulcatis. 



Hab. Cape of Good Hope, 120 fathoms. 



Dredged with the preceding species, but very different in character, and belonging 

 more to the type of T. caput-serpentis. 



IV. LAMELLIBRANCHIATA. 



1. OSTRACEA. 



71. OSTREA, LinncBus. 



1. Oste^a pyxibata. PI. XXI. Pig. 19. Ostr. testa orbiculari, ina?quivalvi, valva sinistra plana, 

 radiatim costata, costis nodulosis, dextra convexa, radiatim valde costata, costis nodulosis saepe duplicatis, 

 margine ventrali crenulato; sordide fusca. 



Hab. Philippine Islands. 



This singular species appears to be characterized by having the right valve extremely 

 convex, and the left one flat. 



2. PECTINACEA. 



72. HEMIPECTEN, n. g. 



Testa adhserens, insequivalvis, irregularis, hyalina, valva snperiore antice simplici, postice vix auriculata, 

 valva inferiore antice simplici, postice conspicue auriculata, infra auriculam profundi sinuata et denticulata ; 

 cardine edentulo, ligamento leviter marginali, cartilagine parvo in cavitatem centralem. 



This interesting shell is intermediate in its characters between Pecten and Anomia. 

 Like Anomia it is a thin hyaline substance, adhering to some foreign body, and of an irre- 

 gular growth, according to the inequalities of its place of attachment. Like Pecten the hinge 

 consists of a slight marginal ligament, intersected in the middle by a small triangular 

 cartilage, situated in the hollow of a superficial cavity in each valve. The under valve is 

 distinguished by a conspicuous auricle on the posterior side, and beneath this is a sinus so 

 deeply cut in the direction of the hinge-margin as to remind one of Pedum, especially when 

 presented with the under valve closed upon the hollow of the upper one, as in Fig. lb, 2 6 ; 

 and the margin of this sinus, as indicated in some of the Pectens, is furnished with a row of 

 sharp erect denticles. The shell bears some resemblance to Pedum, from the circumstance 

 of there being no corresponding sinus in the upper valve ; but it is apparently only a 

 character of resemblance, not one of affinity. The shell has no umbonal area ; nor are the 

 sides of either valve reflected. 



