42 FOSSIL MALACOSTRACOUS CRUSTACEA. 



Genus — Arch^socarabus, M'Coy. 



Char. Gen. Testa autice dcpressa, plana, margine anteriorc recto, clwiticiilato, rostro 

 parvo, bidciitato; siim ccrvicali profundo, lato; posticu subcylindi-ica, rcgiouibus 

 brancliialibus latissimis. Oculi grandes, reniformes, pedunculis angustioribus. Pedes antici 

 luagni, subchcliforirics, digito mobili longo, curvo, ad marginem anteriorcm manus opposito. 

 Pedes reliqui filiformcs, inermcs, subtriedri. Abdomen semicirculare, glabrum. Sternum 

 segiuentis in medio bituberculatis. 



Species unica. Aroh/eocarabus Bowerbankii, M'Coy. Plate XI, figs. 1 — 5. 



Akcii.eocauabus Bowf.uuankii, M'Coy. Aim. Nat. Hist., 1. c. 



Descr. Carapace about twice as long as it is broad, covered with oval, subsquamiforin, 

 flattened tubercles, their blunt apices directed forwards ; cervical furrow deep and broad ; 

 the cephalic arch, or portion anterior to the cervical furrow, flattened, with a high, abru[)t 

 carina on each side, whicli is polished, and armed with two strong spines ; the scaj)ular 

 arch or posterior portion of the carapace, with the tubercles nuich larger than those on the 

 anterior portion, those on the back being the largest of all ; the cardiac region elevated, 

 the branchial very broad, wholly lateral, and placed almost perpendicularly ; the branchio- 

 cardiac fun'ow distinct, smooth, and polished. Abdomen, including the caudal tin, 

 nearly twice as long as the carapace, semi-cylindrical, smooth, slightly punctated ; cpimeral 

 pieces abruptly narrowed, triangular, falcate, curved backwards, and acute at the apex ; 

 lateral plates of the tail nearly three times as long as they are broad, slightly cm-vcd, 

 gi'anulated ; anterior feet broad, compressed ; the hand very broad, expanded towards the 

 anterior extremity, ^\ith a broad, longitudinal depression ; the anterior margin truncate, 

 toothed, the extreme joint or moveable finger ciu-ved, longer than the anterior tmncated 

 margin of the hand, to which it is opposed for ])rehension ; the arm compressed, broad, 

 longer than the hand ; the remaining legs nearly trictbal, smooth, and polished ; sternum 

 triangular, contracted at the anterior part, each segment having a double tubercle in 

 the centre. Eyes very large, reniform ; the peduncle very short, and not one third 

 as broad as the eye. 



Length of the caraj)ace, about .'J inches. 



