1895.] NATURAL. SCIENCES OF PHILADELPHIA. 189 



1. Prionocrangon ommatosteres Wood-Mason and Alcock, 1891. 



Wood-Mason'and Alcock 1. c. p. 362. Alcock and Anderson, Jour. Asiat. Soe. 

 Bengal, Vol. 63, 2, 1894, p. 152. 



Geographical distribution : Bay of Bengal, 200-405 fath. (Wood- 

 Mason, Alcock, and Anderson). 



PARACRANGON Dana, 1852. 



Dana, U. S. Explor. Exped. Crust. 1852, p. 537. Kingsley, Proceed. Acad. 

 Nat. Sei., Philadelphia, 1879, p. 412. 



Second pereiopoda wanting. Eyes present, free. Carapace with 

 long spines. — Gills unknown. 



a x . Branchial regions not areolate, five — spinous P. echinatus. 



a 2 . Branchial regions traversed by anastomosing ridges, dividing 

 these regions into cells of different sizes; they are armed with three 

 small spines P. areolatus. 



1. Paracrangon echinatus Dana, 1852. 



Dana, U. S. Explor. Exped. Crust. 1852, p. 538, pi. 33, fig. 6. Sthnpson, Boston 

 Jour. Nat. Hist. VI, 1857, p. 497. Kingsley, Bull. Essex Instit. X, 1878, 

 p. 55. 



Geographical distribution: W. coast of North America: Puget 



Sound, Oregon (Dana). 



2. Paracrangon areolatus Faxon, 1893. 



Paracrangon areolata Faxon, Bull. Mus. Comp. Zool. XXIV, 1893, p. 200. 



Geographical distribution : Western coast of Mexico: Tres Marias 

 Islands, 676-680 fath. (Faxon). 



Considerations concerning the geographical distribution of the 



Crangonidoi. 



The geographical distribution of the Crangonidoi shows that only 

 one genus, Pontocaris, no doubt the most primitive, is a true inhab- 

 itant of the lesser depths of the tropics, the two species known being 

 found in 49 and 140 fathoms in the Indo- Malaysian seas. All the 

 other genera are partly confined to the seas of temperate or cold 

 climates, partly there is the main range, and only a few species are 

 present in the litoral of warmer climates. Pontocaris, I believe, 

 must be regarded as a survival in the tropics, and its occurrence in 

 somewhat deeper water, but within the limits of the litoral, shows 

 already the tendency to descend into greater depths developed in 

 many species of the other Crangonidce. None of the other species 

 present in the tropical parts of the world can be regarded as sur- 

 vivals ; they immigrated thither from the more northern localities. 

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