Mr Etluriclije on Fossils from Bowen River Coalfield. 285 



ductus, but it appears to be peculiarly distinctive of P. 

 hracliytliccrus. The length of the hinge line varies according 

 to age, in large and old individuals it becomes longer, and the 

 shell, which is very convex and geniculate, loses some of its 

 convexity, and widens out likewise. 



In describing this species Professor Morris, F.G.S., referred 

 to it two shells of very different aspect and state of preser- 

 vation. One of these is a cast in sandstone, showing the 

 general form, and more particularly the channels formed by 

 the decurrent bases of the spines. The other specimen is a 

 decorticated silicious cast, and displays the internal characters 

 of both valves to great perfection. On the ventral valve are 

 exposed the node-like prominences of the cardinal muscles, 

 the scars of the more elongated adductor muscles, and the 

 internal cast of the beak. The dorsal valve shows the scars 

 of the adductors, and the cast of the septum, which in this 

 individual reaches almost to the front margin of the valve, 

 an unusual length in the genus Productus. The vascular 

 impressions are also preserved and come very far forward 

 like the septum. These details are important as will be seen 

 from the sequel. 



In his recently published work on the " New South Wales 

 Fossils of the Clarke Collection," Professor De Koninck has 

 expressed an opinion that the two shells in question referred 

 by Morris to P. Irachytlueims are different, and do not belong 

 to the same species, one being possessed of a short septum in 

 the dorsal valve, and less marked muscular scars, the other 

 on the contrary with a very long septum, and strongly marked 

 scars. In working out Mr Jack's Proditcti it became essential, 

 for anything like a correct determination of the specimens, 

 that some more satisfactory solution of this subject than 

 mere opinion should be arrived at. 



In the first place I endeavoured to obtain access to Mr G. 

 Sowerby's type specimen, contained in the collection made 

 by Dr C. Darwin, F.E.S., but although the latter most cour- 

 teously informed me of the supposed whereabouts of his 

 collection, it cannot, after a thorough search, be found, so that 

 I am afraid this, and the other specimens, all of them of 

 great interest, must be accounted lost. Next in order of 



