On some Nevj Marine MoUusca. 61 



Shell small, thick, sub-orbiculate, scarcely gibbous, slightly- 

 quadrate, whitish, spotted black purple posteriorly ; radiately 

 ribbed, ribs irregular, coarsely nodosely granular ; ribs often 

 divided towards the margin, anteriorly and posteriorly di- 

 varicately and bifurcately plicate ; umbones acute, slightly 

 curved; lunule widely ovate, purple; margins thickened, 

 very flexuous, interior snowy white; teeth thick, con- 

 spicuous. 



There is a Circe something like this figured in Keeve 

 (Icon, v., fig. 21; and identified with G. gihha occurring in 

 the Red Sea and Philippines. It may be the species here 

 described, but it is quite distinct from C. gihha. The difier- 

 ences from both tigures and descriptions are as follow : — 

 It is smaller, almost orbicular, has a series of divaricating 

 ribs sloping away on hoth sides at an acute angle from the 

 first and last central ribs, giving rise to a sculpture like the 

 genus Pythina. 



Arca M'Coyi, n.s. A. t alha, ijeriostraca fiisca plv^ 

 minusve induta, ohlonga, quadrata, medio sinuata et 

 hiante, postice latiore et carinata, confertissime concen- 

 trice granulose costata; granulis suhspinosis, rotundatis, 

 ohtusis, supr. carin. longiorihus et radiathn dispositis ; 

 U7)ihonihus parvis, acutis, planatis, curvatis, area angusta, 

 postice attenuato ; dentihus parvis linea curvata dispositis ; 

 iinarginihiis denticulatis, pagina, interna, nitente, nivea. 

 Long. 7, Lat. 14, Alt. 6. Var ex, N. S. Wales, tumidiorihus. 



Shell white, more or less covered with a dusky periostraca, 

 oblong, quadrate, sinuate and gaping in the centre, broader 

 and keeled posteriorly, very closely concentrically granu- 

 lously ribbed ; granules sub-spinous, rounded, obtuse, longer 

 upon the keel and radiately disposed, umbones small, acute, 

 flattened at the sides and curved ; area narrow, attenuate 

 posteriorly ; teeth small and disposed in a curved line, 

 margins d.enticulate ; internal surface white and shining. 



This shell is so near Arca gradata (Brod. of West 

 Columbia) that I doubt if it be distinct. The species have a 

 wide distribution. The E. Indian A. imhricata, Brug., and 

 the West Indian A. trapezia, are common in Australia. 



PectUnculus flabellatus, n.s. P. t. kite orhiculari, 

 poMlo vero transversa^, crassa, tumidiu^cukc, radiatini 

 valide costata ; costis 25 — 35, latis, planatis, cetaie antice et 

 postice confertis; marginihus late denticulatis; dentihus 

 card. 16 — 20, crassis ; a2ha, intense fulva, intus tincta et 



