32 FOSSIL MALACOSTRACOUS CRUSTACEA. 



and polished, and, like the rest of the crust iu all parts, minutely punctate. The arm half 

 as lon^ again as it is broad, with a tubercle on its antero-interior ande, and a series 

 of veiy small tubercles on the upper and under margin ; the wrist as long as it is broad, 

 with three prominent, shai-p, flattened, triangular spines on the anterior margin, of which 

 the nnur one is the smallest ; the hand smooth, convex, with a small tubercle near the 

 articulation of the moveable finger ; the immoveable finger becomes broader towai-ds the 

 extremity, where it is obliquely truncate, and very evenly seven-toothed ; the moveable 

 one toothless, curved, and pomted, the cm-ved extremity meeting the oblique, toothed 

 portion of the other ; the hand is marked with very regular, minute marblings, in 

 longitudinal hues, which are of two distinct hues, the lines and transverse markings being 

 pale, the interspaces darker brown, and where a portion of the crust has been broken, the 

 subjacent cast, probably covered still with fossilized coloming membrane, exhibits a 

 similar pattern. The remaining feet, as far as can be ascertained from the specimens 

 before me, are of moderate length, smooth, somewhat triedi-al ; and the posterior two 

 pairs smaller ; these were, doubtless, reverted over the back when hving, as in the recent 

 allied forms. Abdomen in both sexes with all the segments distinct and sepai'ate; 

 that of the male rather narrow, broader at the base, the first six segments broader than 

 long, in a diminishing ratio forwards ; the seventh nearly twice as long as broad, rounded 

 at the anterior margin ; the sixth segment with a small intercalary piece on each side at 

 the anterior angle. In the female the abdomen is twice as broad as in the male, and 

 the intercalary a})pendages to the sixth segment larger ; the terminal joint semi-oval, as 

 broad as it is long. 



Length and breadth of carapace, I "5 inch. 



The young state of this species difiers so much from the adult, that, but for the 

 comparison of a series of specimens exhibiting its consecutive conditions, it might readily 

 be taken for a distinct species. Many of the tuberosities which arc distinct, and even 

 ])rominent in the young animal, are lowered, expanded, and some of them even lost, iu the 

 adult. The gastric region has eight distinct elevations, of which only the anterior 

 and posterior pairs (the epi- and meta-gastric), ai-e conspicuous in the adult. The 

 six principal ones form a transverse hexagon, the t^\o ])osterior being considerably larger 

 and more prominent than the others. The vu'ogastric lobe consists of a linear, transverse 

 series of five small tubercles, ^^•hich ultimately become nearly obsolete ; the tubercles of the 

 anterior portion of the branchial are two pairs, the posterior ones being the larger ; and the 

 epicardiac is wholly occupied by one large, rounded elevation ; the posterior rugose portion 

 of the branchial is also more regularly elevated transversely, and the sulcus separating this 

 from the anterior is less deep and distinct than in the adidt ; the metacardiac lobe is small, 

 slightly elevated posteriorly, and polished. 



There is a single specimen of this species in the Ihitish INIuscum, and they are numerous 

 in the collections of Mr. Eowerbank and Mr. Wetherell. I have given figures of specimens 

 of various ages, for the pmpose of comparison. 



