340 PROCEEDINGS OF THE GEOLOaiCAL SOCIETr. [April 24, 



valve ; umbones central, slightly acute and anterior ; posterior and 

 ventral margins equally rounded and smooth ; hinge-line straight, 

 rounded at the angles, giving the shell an almost circular appearance. 



Obs. It is to be regretted that we have not a particle of the 

 original shell wherewith to recognize the nature of the markings, or 

 even the ventral margin to aid us in determining whether the inner 

 edge was crenulated or plain ; externally the shell appears to have 

 been smooth or delicately concentrically marked. The cast of the 

 hinge-line is such as to prevent our determining any teeth below the 

 junction of the two valves. 



In outward form this shell much resembles Lucina (Codallia) 

 ^ercrassa, Stol., from the Arrialoor Group (India) ; and the shell is 

 nearly equal in length to that of this species, but not so high. The 

 paUial line appears to be simple ; and the muscular impressions re- 

 semble those of Pectunculus. Some Axineai from the Indian Creta- 

 ceous rocks, but for their size, would very closely resemble this sheU. 

 "We possess one specimen only, and that a cast of one valve. Figure 

 reduced |-. 



Loc. Maryborough. Form. Cretaceous. 



CtrcxiLLiEA EOBTJSXA, Ether. PL XX. fig. 1. 



Shell trapeziform, rhomboidal, elongated, with valves ornamented 

 with thirteen or fourteen thick costae or ribs ; hinge-area moderately 

 wide, with four horizontal teeth ; umbones much incurved. Unfor- 

 tunately this form does not possess any shell, occurring as a cast 

 only, but distinctly showing the place of the well-pronounced ribs 

 and teeth. 



Obs. In form C. robusta resembles C. oblonga, from the inferior 

 Oolite, and casts of O. Beaumontii, D'Orb., from the lowest White 

 Chalk or beds equivalent to our Chalk marl and Coprolite series ; but 

 the external shell must have been very different when living. 



Loc. Maryborough. Form. Cretaceous. 



CucTJLL^A cosTAXA, Ether. PI. XX. fig. 2. 



Shell deltoid in shape, nearly equilateral ; umbones large and 

 very distant ; the ligamental area wide ; hinge-line straight (teeth 

 not seen in this specimen*); pallial line straight; anterior and 

 posterior sides truncated (in the cast) ; ribs well defined on remain- 

 ing portion of shell, perhaps eighteen to twenty in number, with 

 transverse costse between the ribs ; the ventral margin appears to 

 have been closed. 



Obs. This species is abundantly represented in these rocks, but all 

 in the form of casts ; we are, however, enabled to figure a small 

 portion of the shell which remains upon the specimen, and suffices 

 to indicate that it possessed strong or well-defined ribs and slightly 

 cancellated interspaces. 



Loc. Maryborough, Form. Cretaceous. 



* A specimen in the collection shows thi'ee horizontal hinge-teeth along the 

 posterior edge of the left yalye. 



