18 THE VOYAGE OF H.M.S. CHALLENGER. 



idea is supported by a closely analogous form taken in the West Indies during the 

 "Blake" expedition under the superintendence of Professor Agassiz, and named by 

 Professor Alphonse Milne-Edwards Pylochrfes agassizii. 



Family Thalassinidj. 



Carapace produced anteriorly to a point in advance of the frontal margin ; dorsally 

 flattened. Eyes small ; ophthalmopoda cylindrical. First pair of antennae having the 

 flagella long ; second pair without a scaphocerite. 



First pair of pereiopoda unequal, imperfectly chelate, the pollex being shorter than the 

 dactylos. 



The four following parrs of pereiopoda not chelate, terminating in a long dactylos ; 

 outer rami of the rhipidura without diaeresis, slender, rigid, pointed. Telson without 

 diaeresis, rigid, obtuse, pointed. Branchiae complex, trichobranehiate at the base, and 

 phyllobranchiate on the exterior of each plume. 



This family corresponds with Dana's, and contains, so far as research has yet proved, 

 only a single genus. 



Th a lassina , Latreillc. 



Geographical Distribution. — A very fine specimen of one species of this genus, 

 measuring 225 mm. in length, was procured' at Kaudavu, one of the Fiji Islands. It 

 has been preserved in a bottle with fresh water prawns, and, not being labelled as coming 

 from any station, was, I presume, procured from the natives, and not dredged. Milne- 

 Edwards records it from the coast of Chili, while Desmarest states that it comes from the 

 Indian seas. Heller, in the voyage of the Russian frigate " Novara," obtained it from the 

 Nicobar Isles. Although the localities recorded are not numerous, they are sufficient to 

 show the very wide area over which the animal is distributed, and if, as I am stront>iv 

 induced to believe from the description given by Heller in the work quoted, TJialassina 

 ■maxima is only a smooth variety of Thalassina scorpionoides, and the little Thalas- 

 sina gracilis of Dana only the young of this same species, then we shall find that the. 

 geographical distribution extends from Singapore to Sydney, and across the Pacific 

 and Indian Oceans. Even if these two sj^ecimens be distinct, their separation is not 

 great, for the young, when only an inch and a half long, as is that of Thalassina 

 gracilis, if not identical, must closely approximate to it in form ; while Tludassina 

 ■maximct appears to lie only a less pronounced specimen of the typical species. A 

 genus that is represented by a single species, the distribution of which is so very 

 wide, would, we should presume, have structural conditions decidedly favourable to 

 natural acclimatisation. 



