156 THE VOYAGE OF H.M.S. CHALLENGER. 



circumscribing th(> luiuile. However, the dentition is not absolutely identical, although 

 after the same type. 



In Callocardia guttata,^ dredged off the island of Quelpaart, south of the Korea, in 

 48 fathoms, the only species as yet described, and of which but a single left valve exists, 

 there are two cardinal teeth, of which the posterior is long, lamellar, slightly arcuate, 

 parallel with the dorsal line, and having the edge produced into two denticles. The 

 anterior tooth is very complicated, being thin, prominent, angularly bent in the middle, 

 with the margin produced into four unequal cusps. The ligament is rather long, and 

 situated in a narrow deep groove upon the margin, so that if the valves were closed Ijut 

 very little of it would be visible. 



It will thus be seen that the present species differs somewhat from Callocardia in 

 dentition, in its coarser sculpture, and its more external ligament. It might perhaps with 

 the same propriety be considered a large form of Kelliella, agreeing equally well with 

 that genus in dentition, form, and luuule. 



The two following species bear a still closer resemblance to Kelliella both in size and 

 sculpture, so that it becomes questionable whether there be sufficient ' grounds for 

 separating that genus from Callocardia. 



Callocardia (?) i^acifica, n. sp. (PL VI. figs. 9-9/->). 



Testa parva, globosa, tenuis, fragilissima, alba, hie illic zouis angustis pellucidis, 

 hand conspicuis ornata, concentrice regulariter tenuiterque striata, insequilateraUs, 

 transversim ovato-rotundata. Margo dorsi posticus subhorizontalis, aliquanto arcuatus, 

 anticus brevior, niagis obliquus, subrectus. Latera rotundata, anteriori angustiori. 

 Umbones prominentes, valde incurvati, baud contingentes, partem anticam versus eonspicue 

 versi, ad apicem opaco-album obtusi. Lunula magna, hand impressa, stria tenui 

 circumscripta, cordata, lateriljus valde convexis. Cardo ex dente unico obliquo 

 lamellar! in valva sinistra pone umbonem sito, sulcoque elongate antice irregulari 

 profundo compositus. 



The shell is longer than high, excessively thin and fragile, oblong rounded, a little 

 narrower in front than behind, and consequently more acutely curved. It is jDrettily 

 ornamented with milky white and pellucid zones, and sculptured with fine concentric striae. 

 It is ineciuilateral, the anterior side being much shorter than the posterior, considerably 

 inflated, and glossy. The umbones arc large and prominent, not contiguous, and much 

 curved over towards the lunule. The latter is large, not at aU sunken, heart-shaped, 

 the outline, defined by a very fine stria, Ijeing much excurved. The dorsal margin is 

 long behind, moderately arcuate and but very, slightly ol)lique ; in front it is shorter, less 



' A. Adums, Ann. and Mag. Nut. Hist., 1864, vol. xiii. p. 307. 



