loO THE VOYAGE OF H.M.S. CHALLENGEE. 



Venus (Chione) mindanensis, n: sp. (PL III. figs. 4-4?>). 



Testa subquadrata, auticc ab apicc oblique subtruncata, postice inferue producta et 

 paululum acuminata, valde insequilateralis, costellis radiantibus tenuil)U3 lirisquc concent- 

 ricis iniequalibus subdistaiitibus coucinne caucellata, sordide albida, versus umboues plus 

 miuusve rubesceus. Lunula elongato-cordata, bene defiuita. Area parva, linearis aut 

 nulla. Dentes cardinales in valva dextra tres, quarum postremus paulo maximus, alii 

 duo subparalleli, graciliores. In valva sinistra duo anteriores valde divergentes ; anterior 

 elongatus, lamellseformis, tertius posticus elongatus, gracilis. Impressio muscularis 

 anterior elongata, subpyriformis, quam posteriori paulo minor. Sinus pallii perbrevis. 

 Margo valvarum intus minute crenulatus. 



The form of this species is that of an irregular quadrangle, of which the anterior slope, 

 in conjunction with the posterior dorsal margin, forms at the beak one angle which is 

 almost but not quite so acute as a right angle. 



The posterior dorsal margin is only slightly oblique and arcuate, curving gently inti> 

 the lateral margin, which, together with the ventral edge, forms a somewhat sharply 

 curved extremity, rather low down. The anterior slope descends in an abrupt manner, 

 is gently convex, and rounds into the lower margin, rather less acutely than at the hinder 

 extremity. The umbones are fairly prominent, situated very forward, and are well 

 incurved. The lunule is distinctly defined by a deep stria, elongate-cordate in shape, and 

 sculptured with five or six fine radiating costellsB which, being crossed by the lines of 

 growth, become subgranulose. The radiating ridges which ornament the exterior surface 

 are fine, but not crowded, regular towards the umbones, but further down the valves other 

 intercalary ones are met with which are rather finer. A few of the costellse near the 

 lunule are a trifle stouter and more approximated than the rest. The concentric lirae ai'e 

 thin, crenulated by the radiating riblets, reflexed towards the beaks, especially anteriorly, 

 where they are appressed upon the ribs above. They appear to be comparatively further 

 apart during the earlier stages of growth, and become more numerovis and crowded as the 

 shell increases. They difter in thickness, and their number is variable. The hinge is not 

 powerful, and consists of three teeth in each valve. Of those in the right the hindmost is 

 slightly the strongest and subparallel with the ligamental groove, the two others, of which 

 the front one is the more slender, incline the oj)posite way, and are in a line with each 

 other and almost with the anterior slope. The anterior tooth of the left valve is lamellar, 

 subparallel with the margin, and elongate ; the central one located just beneath the beak, 

 is short, thicker, and slopes in the opposite direction, and the hindmost is very slender 

 and borders the ligamental groove. The dentic-ulation of the margin of the valves is 

 very minute, especially posteriorly. 



Length 8 mm., height 7, diameter 4. 



