SALTER PELTOCARIS. 87 



ornament to the larvae of that group. Unlike most Crustaceans* 

 from the old rocks, it is extravagantly ornamented, with long forked 

 spines. Were it not for the figure of von Meyer quoted above, 

 which shows a considerable amount of ornament in a species of the 

 Eurypterus group, it would have been impossible to have so assigned 

 it. I believe it to be the central lobe of the abdomen of a trilobate 

 Eurypterus or allied genus, and shall so describe it. 



E. horridus, axi corporis (solum conservato) subcylindrico, annulis rugosis 

 spinosis ; tubercula in utroque segmento 4, quorum 2 centralia brevia, lateralia 

 longispinosa, spinis bifurcatis et ad basin bispinulosis. 



The length of the fragment, including five rings, is \\ inch; and 

 the breadth of the axis, without the long forked spines, is |ths of an 

 inch. The forked spines are -|ths of an inch each, and have at their 

 base, front and back, two other smaller spines. 



Locality. In ironstone, North Staffordshire (Museum of Practical 

 Geology). Another specimen, as above noted, occurs in the Hope 

 Cabinet, Oxford ; its locality is uncertain. 



On Peltocaris, a new Genus of Silurian Crustacea. By J. W. 

 Salter, Esq., F.G.S., A.L.S., of the Geological Survey of Great 

 Britain. 



[Bead May 21, 1861.] 



In a paper on Oraptolites from the Anthracite-shales (Llandeilo- 

 flags ?) of Scotland (Quart. Journ. Geol. Soc. vol. viii. p. 391), a 

 figure (pi. 21. fig. 10) was introduced of a minute Crustacean, the 

 affinities of which were doubtful, but which nevertheless had much 

 resemblance to Dithyrocaris, a Carboniferous fossil. That specimen 

 was imperfect ; but one or two since collected in Dumfriesshire are 

 more complete ; and, lastly, a beautiful and perfect example has been 

 given to the Museum of Practical Geology, through the kind offices 

 of Mr. James Young, of Glasgow. 



Fortunately, since I described the above-mentioned little Crus- 

 tacean as Dithyrocaris ? aptychoides, I have had occasion to study a 

 large series of Silurian Crustacea, which have, in their turn, furnished 

 the data whereby to connect this old Phyllopod with the modern 

 Nebalia and Apus ; and I propose in describing this genus to notice 

 them, as chronological as well as zoological links, believing that such 

 illustrations of the theory of Mr. Darwin may best serve to give the 

 data whereby to confirm or refute his masterly hypothesis. 



Peltocaris, gen. no v. 



A small Phyllopod, with a round, shield-shaped carapace ; bivalved, 

 the valves open and imperfectly joined along the dorsal line ; deeply 

 emarginate in front, the excavation so formed being filled up com- 

 pletely by a parabolic plate, which is the analogue of the rostrum, 

 and completes the broad oval shield. 



* There are only a few living Crustaceans which show such an ornament ; 

 the Litkodes described by De Haan, in the ' Fauna Japonica,' is one of them. 



