268 CARBONIFEROUS LAMELLIBRANCHIATA. 



in their respective catalogues. They cannot have been correct ; for it would be 

 unlikely that very young examples should possess the same characteristics which 

 are shown in the adult, if the peculiar shape and marking of C. ventricosa were 

 due to deformity. 



There seems to be a fair amount of variation amongst the specimens collected. 

 PI. XXIII, fig. 3, is relatively much more transverse than the type, but it is a 

 much larger shell, and this may account for it. The depth, number, and position 

 of concentric grooves also vary. In young specimens one appears much closer to 

 the umbo than is seen on the adult examples, showing that these grooves 

 probably became filled up or altered during the process of growth. 



In G. corrugata, M'Coy, the tendency to deep, occasional, concentric grooves 

 becomes a regular character, but the shapes of the valve in the two species have 

 nothing in common. 



Cardiomorpha limosa, Fleming, sp. Plate XXI, figs. 7 — 11. 



Corbtjla limosa, Fleming, 1828. Hist. Brit. Animals, p. 246. 

 Cardiomorpha oblonga, Young and Armstrong, 1871. Carb. Poss. W. Scotland, 



p. 50. 



Specific Characters. — Shell small, transversely ovate, gibbose, somewhat inequi- 

 lateral. The anterior end is well developed ; somewhat narrower from above 

 downwards than the posterior ; gradually compressed into the margins, but above, 

 beneath the umbones, it is concave, so that the anterior part of the hinge-line 

 forms a central elevation. The border is elliptically curved, and passes without a 

 break into the ventral border, which is slightly curved, but becomes more convex 

 at each end. The posterior end is short, obliquely truncate above and rounded 

 below, and forms an obtuse angle with the hinge-line. This is arcuate, but pro- 

 duced posteriorly, and this portion is nearly straight and somewhat depressed. 

 The umbones are gibbose, slightly prosogyrous, contiguous, and elevated above 

 the hinge-line. They are situated a little in front of the middle of the shell, and 

 the anterior border is much more apparent than the posterior. The umbonal 

 swelling becomes rapidly gibbose, but is not of large extent, the valves being 

 rapidly compressed into the borders. The greatest gibbosity is at the junction of 

 the upper and middle thirds of the shell. In adult specimens there is an oblique 

 groove, which passes from the umbo backwards and very slightly downwards to 

 the posterior border at a small distance below the upper border. 



Interior. — The muscle-scars have not yet been exposed. The hinge is 

 edentulous, with a narrow groove above, between it and the umbones, for the 



