REPORT ON THE LAMELLIBRANCHIATA. 85 



terminates in a much more acute extremity, and indeed might be described as subrostrate. 

 The posterior slope descends rather suddenly, and is only a little arcuate, the front margin 

 being less oblique and more excurved, except in the lunula r region, where it is slightly 

 concave. The ventral outline is regularly and widely curved except near the liimlcr end, 

 where it is feebly sinuated, which gives the subrostrate appearance to that portion of the 

 shell. The lunule is lanceolate, narrow, and bounded by a raised ridge on each side. 

 There is but a single cardinal tooth in the left valve, about equal in size to either of the 

 two in the right valve, which are divergent and united at their upper extremities. The 

 anterior does not stand separated, but is united to the ridge which forms the inner side 

 of the lateral groove. Those on l)oth sides commence at the beaks, extend a considerable 

 way down the dorsal margin, and are wide and deep, receiving the i^rominent 

 corresponding margins of the left valve. The internal ligament is elongate, narrow, and 

 posterior to the cardinal teeth. The muscular scars and pallial impression are not 

 clearly definable owing to the condition of the interior of the valves. The posterior of 

 the former appears to be pyriform, rather large, and broader than the front one. The 

 sinus in the mantle line is probably large. 



Length 3f mm., height 3, diameter 1^. 



Habitat. — Flinders Passage, north of Cape York, North Australia, at a depth of 

 7 fathoms. 



The line on each side parallel with the dorsal margin shown in fig. 1 is merely the 

 inner edge of the hinge-plate, which is visible externally owing to the transparency of the 

 shell 



Semele [Ahra) braziliensis, n. sp. (PI. V. figs. 2-26). 



Testa sequilateralis, compressa, tenuis, alba, pellucida, concentrice exiliter striata, 

 nitida, transversim elongata, postice acuminata, antice latior, rotundata. Margo 

 dorsalis utrinque fere rectilinearis, pone obliquior quam ante. Area elongata, planata. 

 Umbones centrales, parvi, acuti. Lunula angusta, baud profunda. Dentes cardinales 

 valvse dextrse subsequales, divergentes, superne conjunct!. Fossae laterales angustse, 

 postica ad umbonem baud pertingens. Ligamentum internum valde obliquuni, 

 angustum. Sinus pallii profundus, ad extremitatem subacutus. 



The shell is very thin and fragile, transparent, equivalve, flattened, glossy, striated 

 with very fine lines of growth, and sculptured with microscopical longitudinal stria? 

 not visible under a simple lens. The form is transversely elongate, broad and rounded 

 in front, and wedge-shaped posteriorly. ' The dorsal margin is peculiarly rectilinear on 

 both sides of the beaks, a little more oblique behind than anteriorly. On the former side 

 there is a narrow flat dorsal area reflexcd almost at right angles to the rest of the 



