284 Proceedings of the Royal Physical Society. 



referable to this species, if species it be, and not, as Professor 

 De Koninck has pointed out, only a form of P. 'brachythmriis 

 (G. Sow.). The ventral valve of the Queensland example, judg- 

 ing from the cast, was very much vaulted and covered with 

 the elongated tear-like bases of spines disposed irregularly, 

 but in the greatest number over the visceral portion of the 

 valve, and on the ears. 



The form of the dorsal valve is peculiar, on account of the 

 marked concavity, following closely the curvature of the 

 ventral valve, and uniting with the latter in its front pro- 

 longation, which is almost at right angles to the body of the 

 shell. Besides the tear-like spines, the shell appears to have 

 been covered with delicate vertical striae. 



In the only specimen which has come under my notice, 

 the spine bases are finer and more numerous than repre- 

 sented in the figure given by De Koninck. 



Loc. and Horizon. — Pelican Creek, two and a half miles 

 above Sonoma road-crossing (Marine Series, No. 59). 



Collector. — E. L. Jack, Esq. 



Productus hrachythcerus — G. Sowerby. — PL VIIL, fig. 16 ; 

 PI. IX., figs. 17, 18. 



P. hrachythcerus, G. Sow., Darwin's "Geol. Obs. Volcanic Is. , " 1844, p. 158. 

 „ Morris, Strzelecki's " Phys. Descrip. N. S. Wales," 1845, 



p. 284, t. 14, f. Ac (non 45). 

 „ De Koninck, Mon. Productus et Clionetes,1847, p. 102, 1. 10, 



t la and h (non Ic and d). 

 P. undulatus, M'Coy, Annals Nat. Hist., 1847, xx., p. 236, t. 13, f. 2. 

 P. hrachythcerus, De Koninck, Foss. Pal. Nouv-Galles du Sud., 1877, pt. 3, 

 p. 198, t. 10, f. 4 and 4a, t. 11, f. 1. 

 „ Etheridge, jun., Cat. Australian Foss., 1878, p. 51 {for 



synoiiomy). 



Ohs. — This characteristic Australian species is represented 

 in Mr Jack's collection by specimens from two localities. 

 All who have written on P. hrachythwrus lay stress on the 

 shortness of the hinge line, as compared with the width of 

 the front. This, with the elongated decurrent bases of the 

 spines, forming channels in the shell, are particularly charac- 

 teristic points in G. Sowerby 's species. The channelling of 

 the shell by the spine bases is seen in many species of Pro- 



