REPORT ON THE LAMELLIBRANCHIATA. 185 



apparently distinct from any known form. It is rather convex, rounded and concave in 

 front of the umbo, where there is a small deepish lunule. It is sculptured with about 

 fifteen flatly rounded radiating ribs, which arc al)sent down each side, and concentric 

 elevated lines of growth. There is a single cardinal tooth in this right valve, and a short, 

 erect, subequidistant lateral on each side ; the lower margin is rather strongly denticulated 

 where the ribs terminate, but smooth at the sides where the costae are wanting. 



Lucina (Loripes) desiderata, n. sp. (PI. XIII. figs. 10-lOa). 



Testa parva, tenuis, iufequilateralis, alta, postice radiatim impressa, antice profunda 

 lunulata, albida, concentrice tenuissime lirata, liris numerosis sublamelliformibus prope 

 lunulam et marginem dorsalem posticum cristatis. Margo dorsi anticus brevis, valde 

 excavatus, posticus longior, rectiusculus, vel parum convexus. Latus anticum regulariter 

 curvatum, posticum ad terminum impressiouis leviter sinuatum. Umbones parvi, acuti. 

 Lunula elongata, Isevis, conspicue excavata, areaque postica, angusta, Isevis, valde impressa. 



This little species is higher than long, somewdiat inequilateral, moderately convex, 

 thin, white, and marked with a shallow radiating dej^rcssion down the posterior side, 

 producing a faint indentation or sinuation in the outline, which, along the lower portion 

 and in front, is regularly circularly curved. The sculptures consists of numerous very 

 fine thin concentric lirse, which, especially towards the ventral margin, become some- 

 what lamelliform, and towards the lunule and hinder dorsal slope are elevated into 

 small, thin, dentiform projections. The lunule is rather large, smooth, and very deep, 

 and defined by sharp edges. The area is long, narrow, also deepish and circumscribed 

 by acute margins. The beaks are small, sharp, well -curved over the lunule, and consider- 

 ably in front of the middle. The left valve has two small divergent cardinal teeth, 

 separated by a triangular pit, which receives a corresponding tooth in the right valve. 

 The internal ligament is in a deepish groove just within the dorsal margin behind the 

 teeth. The inner surface, owing to the thinness and semitransparency of the valves, 

 exhibits the concentric ornamentation of the exterior, and towards the lower part is 

 somewhat indistinctly radiately substriated. 



Length 3^ mm., height 3f, diameter 2^. 



Habitat. — Station 188, south of New Guinea, in 28 fathoms; green mud. 



This is a small species, resembling in its radiating depression some of the typical 

 forms of Cryptodon. 



Lvcina (Loripes?) jacksoniensis, n. sp. (PI. XIII. figs. 11-116). 



Testa globosa, rotundata, tenuis, subsec^uilateralis, albida vel dilute fusco tincta, 

 incrementi lineis confertis striisque numerosis tenuissimis sculpta. Lunula parva, baud 



(ZOOL. CHALL. EXP. — PART XXXV. — 1885.) Mm 24 



