152 INYERTEIiKATA. 



striae. A set of well-defined regular concentric striae crosses the 

 ribs and interspaces, producing a distinct scalariform structure. 



The cast is smooth or faintly radiated, with a posterior groove 

 left by the muscle-shelf. 



Measurements. Cardino-pallial diameter, 19 mm.; antero-pos- 

 terior diameter, 21 mm. ; thickness (through both valves), 14 mm. 



Affinities and differences. This shell is so very nearly equi- 

 lateral that it might be referred to the genus Pechmculus, but it 

 has the projecting shelly muscular shelf for the insertion of the- 

 posterior adductor muscle as in Cifcullcea. Its globose, nearly 

 equilateral form, sharp ribs with few striations, and the regular 

 cross-barring of the interspaces well distinguish this species. 



From C. rotwidata r Roemer, it is distinguished by its larger 

 size, better-defined ribs, and larger more rounded umbo. 



I have little doubt that the original home of this shell was in 

 Neocomian waters, though now it is only known as a derived fossil 

 in newer Neocomian deposits. 



Localities. In the Black Grit rock, derived blocks, Upware ;. 

 also in the Herrimere Rock. 



CUCUULEA DO'XNTNGTONEXSIS, sp. 110V. 

 (Plate VIII., fig. 9, a, b.) 



Shell globose-quadrate, inequilateral, radiately ribbed. Umbones 

 prominent, rounded, oblique. Anterior side rounded ; posterior 

 obliquely truncated. Hinge line short ; area narrow, marked with 

 angular cartilage grooves. Ribs about 30, equal but becoming 

 faint towards the posterior side ; they are angular in section, mo- 

 derately promineut, and covered with strong secondary striae, 

 which also occupy the interspaces. These are crossed by close-set 

 growth striae. 



Measurements (type from Upware). Cardino-pallial diameter, 

 21 mm. ; antero-posterior diameter, 25 mm.; hinge-line, 12 mm. ; 

 thickness (through both valves), about 20 mm. 



A ribbed species more oblique than the last, and with the ribs 

 more triangular in section and covered, together with the inter- 

 spaces, with numerous and well-marked striae, which are crossed 

 by close-set lines of growth ; also the umbo is less prominent. 



