IV. — On the Anatomy of Libinia emargmata Leach, the Spider 

 Crab. By E, A. Andrews. 



The body of this common crab is spheroidal in form, prolonged 

 in front so that this part has a triangular outline. It is covered with 

 a firm chitinous shell, densely clothed with minute flattened pro- 

 cesses, setse, wdiose edges are armed with spines, and with longer, 

 more hair-like, setfe, similarly armed. The dorsal surface bears also 

 many stouter seta3 with recurved tips. All these processes serve to 

 entangle algoe, hydroids, and dirt. 



The stout carapace completely covers the dorsal surface of the 

 animal and is prolonged between the eyes to form the emarginate or 

 slightly forked rostrum (rs, fig. 1). It is set with numerous blunt 

 spines and divided by grooves into regions, which take their names 

 from the internal organs lying below them. A short transverse 

 groove, part of the cervical groove, near the center of the carapace 

 separates a broad swollen anterior area, the gastric lobe, from a 

 narrow central area, the cardiac lobe. The outward and forward 

 prolongations of this transverse groove, together with a longitudinal 

 groove extending back from each of its ends, separate the above 

 mentioned lobes from the large lateral areas or branchial lobes. On 

 either side of the anterior part of the gastric lobe a small swollen 

 area marks the place of attachment of the large adductor of the 

 mandible, but is known as the hepatic lobe. Above the bases of the 

 legs the carapace is reflected inwards and, passing upwards as a 

 thin, translucent, chitinous membrane (c, fig. l), is attached to the 

 upper edge of the flanks. A large branchial cavity is thus left on 

 each side, betAveen the flanks and the overhanging carapace. Poste- 

 riorly the carapace overhangs the basal portion of the abdomen, with 

 the anterior edge of the dorsal surface of w^hich its delicate reflected 

 portion (w, fig. 1) is continuous (o). In advance of the legs the 

 reflected carapace forms on each side of the body a smaller, flattened 

 cavity, the efterent canal (/, fig. 1), leading from the branchial cavity 

 to the side of the mouth. The entire dorsal surface of the cephalo- 

 thorax is thus protected by the carapace. 



The abdomen is small and flat and closely bent under the body. 

 It is composed of seven joints or segments whose integument is well 



Tkans. Conn. Acad., Vol. VI., 1883. 14 July, 1883. 



