56 NEW-YORK FAUNA — CROSTACEA. 



a large triangular cavity in front. It is by a separation of this rim or border, that the animal 

 is enabled to leave its old shell. The upper surface of this anterior portion is marked by 

 three longitudinal carinae, more or less elevated, and separated in the adult by a deep fissure 

 nearest the central carina, and continuous with the series of branchial openings to be noticed 

 on the posterior portion. On the central carina, the first spinous tubercle is equidistant 

 between the central one and the anterior rounded margin. Central tubercle often effaced. 

 Eyes oblong-lunate, reticulated, scarcely elevated above the shield, and placed exterior to the 

 anterior part of the lateral carina. Posterior portion of the shield produced at the sides into 

 spinous tips, which are minutely serrate, and thickly beset with long hairs. The posterior 

 or abdominal portion trapezoidal, deeply notched behind for the reception of the tail, where it 

 has upturned acute spines on each side. The lateral edges, including these last, have seven 

 ciliated serrated triangular spines ; between these are six flat acute elongated slightly curved 

 movable spines, ciliated on both edges, and gradually diminishing in length from before : the 

 largest of these exceed an inch in length. At the junction of the two large portions of the 

 shield is an irregularly shaped tuberculous spine with a broad basis, denticulate on its edge, 

 ending in an acute point, and suddenly descending behind to the plane of the shell. Six 

 apertures arranged in two longitudinal converging series ; and between them, on the medial 

 line, two minute spinous tubercles, one of which is near the anterior margin, the other just 

 behind the line of the two posterior apertures ; the under side of both portions with scattering 

 hairs. In front of the mouth a pair of feet, with small didactylous claws, which are considered 

 by some authors as antennee ; then follow ten feet, their haunches with a lobed projection 

 covered with long spines over the mouth, and performing the functions of jaws : there are also 

 distant spines on the succeeding joints. In the female, all these terminate in didactylous or 

 multidactylous claws. In the male the anterior pair is of a different configuration (see fig. 

 51.) : the penultimate joint ventricose, with a small tubercle at the apex ; the last joint single, 

 and shaped not unlike the toe of a bird with its claw. The last pair terminates in four mova- 

 ble foliaceous convex joints, which are rounded at tip, and a fifth cylindrical joint which itself 

 ends in two movable claws. Posterior to these pairs is a large foliaceous multiarticulate 

 structure, having at its posterior base the sexual organs. Posterior to this are ten fin-feet, 

 united at their base in pairs, and supporting the gills on their posterior faces. Tail rigid, 

 partially flexible in the living animal, nearly as long as the shield, triangular, rounded and 

 smooth beneath, carinate and spinous above, ending in a sharp point. 



Colo?; of a uniform dark brown ; eyes somewhat lighter ; the abandoned shells of the 

 young white. " ' t \ 



Total length of female, 19-0-22-0; of tail, 9'0-10-0. 

 Extreme width, 9-5. Height, 3' 0-4-0. 



This common species on our shores is known here under the popular name of Horse-foot, 

 on account of its shape, and still retains in some districts the name given to it by the early 

 English colonists, of King Crab, in allusion to its size. The males may be distinguished at 



