CANCROIDEA. 



have the inner margins parallel, but the sulcus near the margin is 

 not parallel to the margin, the two sulci diverging posteriorly. 



This family is closely related to the Corystoidea, and forms one of 

 the connecting links between that group and the Cancroidea; the 

 outer maxillipeds in Cancer and Perimela in projecting over the epis- 

 tome, approach those of Corystes and Atelecyclus, and the narrow 

 form of Perimela has led to its reference in some systems to that 

 group. Through Perimela there is also a transition to Polybius and 

 other genera of Portunidae, in which the outer maxillipeds have a 

 like character, and the general form is also similar. In general 

 outline and convex form the species of Lupa are related to those of 

 Cancer, and our genus Arengeus fails in the prelabial ridge, and thus 

 approximates quite closely to that group. 



GENUS I. CANCER (Leach). 



In addition to the remarks already made on this genus, we observe 

 that the postero-lateral margin is very oblique inward, approximating 

 sometimes to transverse. The regions are indicated by undulations 

 of the surface, and not by trenchant sulci. The area either side of 

 the anterior part of the median region is often somewhat concave. 



The outer antennae have a very broad basal joint, which sets down 

 upon the anterior margin of the buccal area, or with only a very 

 short intervening space ; and the two leave between them a narrow 

 interval which is occupied by the inner antennae. The whole breadth 

 occupied by the pair of outer antennae is less than the breadth of the 

 buccal area. The following joints proceed from the inner side of the 

 basal joint. There is a tooth adjoining the orbit, and three between 

 the outer antennae, the medial of the three largest. In one species 

 the lobes are nearly equal crenatures of the margin. 



Platycarcinus, M. EDWARDS, Crust., i. p. 412. 



CANCER MAGISTER. 



Carapax nuclus, granulatus, paulo convexus, superficie paulo undulatd, 

 lateraliter triangulatus et acutus, margine postero-laterali fere recto, an- 



