56 A HISTOEY OF EECENT CRUSTACEA 



ovate swimming organ. The species are marine or 

 littoral. 



This legion contains four families — Cancridss, Trape- 

 ziidfe, Portunidae, Podophthalmidse. 



Family 1. — Gancridce. 



The carapace is commonly transverse and convex, with 

 the antero-lateral margins arcuate, and armed with several 

 lobes, teeth, or spines. The ' front ' is of moderate width, 

 in general not projecting over the first antennae and the 

 bases of the second, the latter being seldom excluded from 

 the inner hiatus of the orbits. 



In this family are included about half a hundred 

 genera, some widely and conspicuously distinct, others 

 separated by fine and almost inappreciable differences. 

 Thus Mr. Miers observes of Xantho (Leach, 1813), that 

 ' it is connected by almost insensible gradations on the 

 one hand with Lophoxanthus and Xanthodes, on the other 

 with Pano2')eus and Eurypanopeus.' Quite recently the 

 genus Panopem, H. Milne-Edwards, 1834, has been re- 

 viewed by James Benedict and Mary Rathbun. They 

 recognise in it thirty-eight species, and re-include within 

 its boundaries Euri/Huin, Stimpson, 1859, and Eurypano- 

 pens, A. Milne-Edwards, 1880, considering that they have 

 been separated from the parent genus on grounds in- 

 suflScient or untenable. It will, however, be quite be- 

 yond the range of such a manual as this to eater into 

 all the minutias of generic distinctions. Far less can the 

 characters of innumerable species be discussed. Only the 

 specially typical or the specially anomalous forms may 

 court a passing attention. Here and there a comparison, 

 a description, a comment, may indicate the variety of 

 details upon which classification is founded, or may sug- 

 gest the endless opportunities for the exercise of keen 

 eyes and acute minds, which the subject provides. 



Those whose scientific zeal is limited to the desire of 

 having the specimens in a cabinet rightly arranged and 

 ticketed with their proper names are often puzzled and 



