110 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 



HARPAX WALTONI, Lye. Tab. XXXII, figs. 1, 1 a, 1 b. 



Testa (valva dextra) magna, crassa, ovata, convexa, sub-auriculata, late adJierente, 

 radiatim costatis, lamellis incrementi crebris, crassis nodiferis et imbricatis, facie interno, 

 tabula cardinali magno dentibus et foveis longissimis insigni. Valva sinistra depressa, 

 crassa, lamellis ut in valva altera, tabula cardinali dentibus prominentibus, longissimis, 

 obliquis, sulcis conformibus. 



Shell of large dimensions, the right valve with a very large surface of attachment, sub- 

 auriculated, thick, ovate, convex, the surface radiately costated, with thickened, crowded, 

 imbricated and elevated lamellae of growth ; the triangular hinge plate is very large, 

 oblique, transversely striated ; the diverging outer grooves which receive the dental pro- 

 cesses of the other valve are large, deeply impressed, and exhibit in their course three 

 deeper portions or pits adapted to the successive positions occupied by the anterior, pro- 

 jecting or bossed extremities of the dental processes in the free valve ; the adductor scar is 

 very large and posterior. 



The left or free valve is thick, but less convex than the other ; the hinge area occupies 

 upwards of two fifths of the length of the valve ; the ligamental groove is narrow and 

 deeply marked, but the other furrows are superficial ; the outer diverging dental pro- 

 cesses are lengthened and conspicuous, terminating anteriorly in projecting bosses ; the 

 adductor scar is prominent and sub-central. In the specimen figured with the valves in 

 contact, the right valve has adhered to a smaller specimen of the same species, whose 

 exposed inner surface exhibits the usual characters of the left valve. 



Our species is allied to Harpax calvus and H. scnescens, Desl., from the Middle Lias 

 of Calvados, but has more prominent rugose lamellae, and a larger hinge area in both the 

 valves. In the left valve the anterior termination of the dental processes in bosses with 

 corresponding pits in the furrows of the other valve, has no counterpart in the figures or 

 descriptions of M. Deslongchamps, but as they do not appear to be equally persistent in 

 all specimens their importance can only be small. 



Geological Positions and Localities. The Forest Marble of Farleigh Wick, Somerset ; 

 collected by W. Walton, Esq., whose labours have been rewarded by the acquisition of 

 several good specimens. The interiors of the valves of this species have also been observed 

 in the Great Oolite of Minchinhampton ; in these instances, however, their external 

 surfaces could not be disengaged. 



GERVXLLIA WALTONI, Lye. Tab. XXXII, figs. 4, 4 a, b. 



Testa frfigili, ovato-oblonga, valva sinistra antice convexa, postice explanata in alam 

 brevcm producia, umboni prominente, apicc acuto, subterminali, ala antica brevi, margins 



