124 MOLLUSCA FROM THE GREAT OOLITE. 



Pholadomya solit aria. Tab. XII, figs. 2, 5 ? var. of P. producta, Sow. 



Testa ovato-subglobosd ; umbonibus magnis, latis, mediants; lateribus brevibus, postice 

 lavi, aperturd angustd ; costis (7) perpendicularibus elatis approximatis, cequalibus, Iceviter 

 impressis ; plicis concentricis tenuibus. 



An ovately globose large species, with elevated median and broad umbones ; the sides 

 of the shell are short, the posterior side being destitute of costae, its aperture is incon- 

 siderable ; the costae (7 in number) are large, equal, but little divergent, and only slightly 

 indented by the concentric plications, which latter are not conspicuous. 



The height always exceeds the lateral diameter, and that through both the valves, the 

 two latter measurements being nearly equal. 



The combination of broad umbones, with equal little impressed perpendicular costae 

 only slightly radiating, together with the short but not truncated sides, will suffice to 

 distinguish it from contemporaneous species. 



Geological position and localities. — All our specimens are from the Minchinhampton 

 district, they have been procured at several localities in oolitic sandstone a little higher 

 than the fullers' earth, and obtained by well sinkings, they were unaccompanied by any 

 other fossil. 



Pholadomya Heraulti, Ag. Tab. XV, fig. 4, var. Tab. XII, fig. ] . 



Pholadomya Murchisoni, Ag. Etud. Crit., p. 79, t. Ac, f. 5, 7- 



— — Eoemer. Nordd. Ovl., p. 128, t. 15, f. 7. 



— Heraulti, Ag. Etud. Crit., Appendice, 1845. 



Testa ovato-globosd ; umbonibus magnis anticis, serratis ; area cardinali magna, elongatd, 

 latere postico modico hiante, latere antico brevi, costis {circa 9) obliquis, elevalis plicis 

 longitudinalibus impressis ; costd prima obscurd, costd secundd majord et elevatd. 



Shell ovately globose ; umbones large, anterior, and serrated ; cardinal area large and 

 depressed, posterior side gaping with a lengthened and moderately large aperture, anterior 

 side short, slightly truncated ; the radiating costae, (usually 9 in number,) are large and 

 elevated, the posterior ones are oblique ; the first is only slightly marked, the second is the 

 largest and most elevated; they are strongly impressed or rendered nodulous by the 

 longitudinal plications ; the two extremities of the shell are destitute of costae. 



This shell is more elevated, and the prominence of the second rib will suffice to separate 

 it from P. Murchisoni, with which it has been confounded. 



Geological position and localities. — Pholadomya Heraulti occurs not unfrequently in 

 certain sandstone beds of the Great Oolite, in Gloucestershire ; also at Blisworth, North- 

 amptonshire, but the dimensions of these specimens are usually small ; in the Inferior 

 Oolite it appears to range throughout the extent of that formation in this country, in 

 which it attains its full dimensions, and is very common. 



