528 CRUSTACEA. 



from the anterior projecting part of the epistome, and the base of the 

 inner antennse is wholly inside of the base of the outer. Spines are 

 situated on the joints, as shown in figure b. 



This species is near the planifrons, but has a narrower and more 

 slender beak, with four spines either side on the beak itself, besides 

 having no prominent spines on the lower margin of the hand. 



Subtribe ill. CABIDEA. 



In arranging the Caridea into groups, much stress is usually laid 

 upon external form and length of beak. The unimportance of these 

 characters might be inferred.* from the fact that they involve no 

 striking variations of structure : nothing but their running parallel 

 with other characteristics of real value could entitle them to para- 

 mount consideration. A survey of the species of a single group, 

 enables us to discover their subordinate rank. In the Crangon group, 

 in which the form is commonly depressed and the beak short, there 

 are species as much compressed and as long rostrate as the typical 

 Hippolyte, with the same form and general habit ; and the depressed, 

 short-beaked Pontoniae graduate into the compressed, long-rostrate 

 Palaemon, by so insensible gradations, and differ from them so little in 

 essential characters, that both groups are parts of a common family. 



The relative positions of the first and second pairs of antennae 

 would seem to be a character of more value. But this position varies 

 directly with the breadth or depressed form of the species ; so that in 

 the same genus Pontonia, as this genus is laid down by Edwards, 

 these antennae may be either in the same horizontal line, or the first 

 more or less over the second. It is not a character indicating supe- 

 riority of grade ; for those Brachyura are of higher rank in which the 

 pairs of antennae are most nearly one above the other, while among 

 the Macroura the reverse is true, to at least a great extent. 



Among the organs of Crustacea, those earliest in development are 

 the mandibles, and any essential differences they present, are, there- 

 fore, of early origin and of a fundamental character, compared with 



