238 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



level of the anterior cardiac region. Eront produced into a lamellar 

 rostrum, of equal length and breadth, grooved in the middle, and 

 terminating anteriorly in a point without any bifurcation. In both 

 the specimens examined the remainder of the fironto-orbital portion 

 of the carapace is imperfect, and partially concealed in the matrix ; 

 but the ocular peduncle was apparently inserted just beneath the 

 rostrum, and the eyes folded back into a slightly concave orbit, the 

 upper edge of which is less advanced than the former. 



Cephalic and meso-branchial grooves deep and distinct ; gastro- 

 hepatic less so ; meta-branchial furrow indistinguishable. 



In the smaller specimen the meta-gastric and uro- gastric regions 

 are separated from each other by a transverse furrow, and a sepa- 

 ration of the lobes in each of these regions is indicated by a longi- 

 tudinal median furrow. In the larger specimen these parts are im- 

 perfect; but the grooves, as far as they can be seen, appear to be less 

 distinct. In both specimens the anterior cardiac region is distinguish- 

 able. The meso -gastric region is triangular in form, with the apex 

 extending forwards between the lobes of the epi- and proto -gastric 

 regions. The hepatic region is small, and has an obtuse spine at 

 its point of contact with the orbits. The upper surface of the 

 carapace is covered with two species of tubercles, the smaller of 

 which are irregularly scattered over it, and the latter more definitely 

 arranged. Two, of a fusiform shape, are situated at the base of the 

 rostrum, one on either side of the median groove, and are followed 

 by five others disposed nearly in a straight line across the carapace. 

 The central one of these is situated in the apex of the triangular 

 meso-gastric region, and is succeeded at a short interval by another 

 and somewhat larger tubercle. The branchial regions on either side 

 also carry five or six tubercles. 



Affinities. — Although the general characters of the carapace (such 

 as its peculiar form, comparative dimensions, the production of its 

 front into an elongated rostrum, &c.) sufficiently indicate the position 

 which this species occupies among the Brachyura, stiU its affinities 

 with existing genera are not sufficiently close to allow of its being- 

 placed among the members of either of them, and I therefore pro- 

 pose to give it the generic title of Mithracites. Fully recognizing 

 the difficulty of obtaining complete generic characters from imperfect 

 specimens of a single species, I have only ventured to give the few 

 following from the scanty material at my command, leaving them 

 to be added to, or modified, if necessary, after the examination of 

 any more perfect examples which may be subsequently obtained. 



Genus Mitkracites. 



Carapace slightly longer than broad, and having most of the 

 regions well defined ; front produced into a rostrum, not bilobed ; 

 orbits shallow, with the under edge anterior to the upper. 



