604 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [May 23, 



the posterior surface up to the margins of the suture. The absence 

 of a dorsal furrow at once separates it from Peltocaris HarTcnessi 

 and P. aptychoides (PL XXY. fig. 6), allied forms of Phyllopodous 

 Crustacea found in the same shales. 



The wedge-shaped suture, which divides the shield of this crus- 

 tacean in front, doubtless corresponds with the suture in the shield 

 of Apus and the nuchal furrow in the Macrurous Decapods. 



A similar line of separation has already been noticed in the shield 

 of Peltocaris aptychoides. (See Mr, Salter's paper in the Quart. 

 Journ. Geol. Soc. vol. viii. pi. 21. fig. 10.) 



Why, it may be asked, does the shield in this old crustacean, and 

 also in P. aptychoides, always separate along this line of suture, and 

 leave the appearance presented in the figure ? (PI. XXY. fig. 4.) 



I can best explain this by referring to the recent Apus, in which 

 the footjaws, branchiae, and abdomen appear to be aU strongly 

 united to the head, and that to the rostral portion of the carapace ; 

 whilst to the far larger posterior surface of the shield the attachment 

 is so slight that specimens always become detached in this manner, 

 and, as in the case of the phragmacone and sheath of the fossil Belem- 

 nite, the soft parts of the animal will often be found in one locality 

 and the carapaces minus the frontal portion in another. 



Such is the case with Dithyrocaris, an allied genus, the organs of 

 manducation of which are seldom if ever found with the shields, but 

 in nodules (probably composed of the soft parts of the animal) in a 

 bed by themselves*. 



It may be interesting to record that among the specimens from 

 Mr. Carruthers's cabinet is a small example of Peltocaris aptychoides, 

 which exhibits the concentric lines of growth as in the Discina-like 

 form herein described. (See Plate XXY. fig. 6.) 



"With the exception of GraptoHtes, fossils are of rare occurrence 

 in the Mofi'at shales. Mr. Salter has, as already stated, describedf 

 two phyllopodous Crustacea, Peltocaris Harhnessi and P. aptychoides. 

 Professor Harkness has found a small Brachiopod {Siphonotreta 

 micula, M'Coy), and Mr. J". Stevens, formerly of Mofi'at, a single 

 specimen of Tentaculites. 



The addition, therefore, of a new Phyllopod is an interesting dis- 

 covery. Erom its resemblance to Discina, I have proposed for it 

 the generic name of Discinocaris, and the specific appellation of 

 Broiuniana after Mr. D. J. Brown, who first drew my attention to it. 



Dimensions. — Diameter of disk-shaped carapace 7 lines, sector 

 one-sixth of its arc. A larger specimen folded together probably 

 measured 14 lines in diameter. 



EXPLANATION OF PLATE XXV. figs. 4-7. 



{Illustrative o/ Discinocaris Brovmiana.) 



Fig. 4. Discinocaris Browniana, H. Woodw. Moffat Shales (Lower Silurian), 

 Dumfriesshire. Natural size. Collection of Mr. D. J. Brown, 



^ Oeol. Mag. vol. ii. 1865, p. 401, pi. 11. 

 t Quart. Journ. Geol. Soc. vol. xix. p. 87. 



