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



Tlie cancellated surface, a feature rather uncommon in this genus, will readily 

 distinguish this from other Atlantic forms. Although the above may not be the full 

 dimensions reached by the species, I am of opinion that it does not attain a very much 

 larger size. 



Circe jucimda, n. sj). (PI. II. figs. 3-3?*). 



Testa rotundata, paulo iuajquilateralis, latere antico postico angustiori, albida, 

 increment! lineis tenuibus, marginem inferiorem versus aliquanto, fortioribus, sculpta, 

 costellis numerosis gracilibus radiantibus granulosis utrinque ornata. Umbones parvi, 

 acuti, incurvati. Margo dorsalis antice vix convexus, leviter obliquus, j^ostice minus 

 descendens, rectiusculus, vel levissime convexus. Ventris margo arcuatus, antice 

 sensim adscendens. Lunula mediocriter magna, linea gracillima impressa circumdata, 

 baud ratiatim lirata. Dentes normales ut in Circe castrense. Margo dorsi posticus 

 valvse dextrse conspicue intus sulcatus, sulco elongate, profundo. 



The valves here described are possibly only the young stage of the species, but the 

 character of the sculpture is sufficiently peculiar that the adult form would be 

 recognisable without much difficulty. It is a roundish species, a little longer than 

 high, slightly inequilateral, the anterior side as usual being the shorter. It is white, 

 somewhat convex, sculptured with fine striae or lines of growth, which become rather 

 coarser as the shell enlarges. In addition there are, on each side, numerous very 

 slender radiating lirae which are a trifle arcuate, especially those upon the anterior end, 

 and, being crossed b)^ the concentric striae, become finely and very prettily granular. 

 The umbones are rather small, acute, curve over towards the anterior end, and are but 

 little elevated above the dorsal line. This is slightly convex, and rather oblique 

 in front, and forms with the slowly ascending basal margin, which is l>roadly curved, a 

 narrower, more acutely rounded end than at the opposite extremity. The hinder slope 

 is less oblique and nearly rectilinear at first, then rounding into the lateral outline. 

 The lunule is moderately large, scarcely sunken, enclosed by a very fine impressed line, 

 prominent along the middle, broadly lanceolate in form, and sculptured onl)^ with 

 the fine lines of increment. The hinge is composed like that of other species of Circe. 

 In the left valve the central tooth is thick, trianoular, and much stouter than 

 either of the two others. In the right valve it is also triangular and thickish, but not 

 much stouter than the posterior, which is rather longer. The hinder dorsal slope in 

 the latter valve is conspicuously grooved within, the groove being elongate and extend- 

 ing nearly to the extremity. In the left valve there is a corresponding elevated ridge 

 between the extreme outer edge of the slope and the inner margin of the hinge-plate. 

 The ligament would be internal, or scarcely visible from the exterior. The anterior 



