1514 CRUSTACEA. 



of the Lalandii of the Cape of Good Hope, or the vulgaris of the Medi- 

 terranean, both gigantic species, sometimes a foot and a half in length 

 independent of the antennse. 



The Astacidae, the remaining family in the tribe Astacoidea, is con- 

 fined almost wholly to the colder waters, and the species are numerous. 



Among the Caridea, the Crangonidse certainly have the precedence. 

 The fact that the first pair of legs have perfect hands, while the other 

 legs are vergiform, shows a relation to the Brachyura, which is evi- 

 dence of superiority. These Crangonidae, thus the highest of the 

 Caridea, are almost exclusively cold-water species. 



In the family Palaemonidae, some genera have the anterior legs 

 furnished with stout hands, while in others the second is the stout 

 chelate pair. The former, for the reason just alluded to while speak- 

 ing of the Crangonidae, and elsewhere farther explained, are superior 

 in rank. It is among these genera of this superior grade, the Alphe- 

 inae, that we find the cold-water and boreal species. The genus 

 Hippolyte alone contains thirty-seven cold-water species, nineteen of 

 which are of the Frigid zone ; and there are only eight torrid species. 



On the contrary, among the Palaemoninae, the inferior group, there 

 are forty-six torrid to twenty-two of extra-torrid ; and only one of the 

 latter is boreal. Species of Alpheus are common in the tropics about 

 coral-reefs ; but the largest species of the genus, two or three inches 

 long, occur beyond the tropics. 



The Penaeidea, the lowest of the tribes of Macroura, are mainly 

 tropical. Yet, the very lowest species (like the lowest Brachyura) 

 occur partly in the colder waters, or even in the Frigid zone. 



XXIII. Comparing the torrid and temperate species of Macroura, 

 we are led to conclude, that the latter are probably most numerous in 

 individuals, and the most bulky in mass. Excepting the Panuliri, 

 Scyllari, and some Palaemons, the tropical species are small, and more- 

 over, they are not particularly abundant about coral-reefs. The 

 species of the torrid genera, Pontonia, (Edipus, Harpilius, Anchistia, 

 Palaemonella, Hymenocera, and Atya, are all quite small, the greater 

 part not exceeding an inch and a quarter in length, and moreover, 

 the tropical Alphei are also small species, as stated above. The 

 Penaeidea are partly larger species. Contrast these particulars with 

 the facts as to the genera of the Temperate zone. Palinurus, Astacus, 

 Nephrops, Paranephrops, Homarus, Arctus, Crangon, and the related 

 genera, Hippolyte, Pandalus, Cryphiops, contain species mostly of 



