Dr. W. T. Caiman on Munldopsis polymorpha. 217 



which the cave communicates with the sea, found there an 

 environment suitable, at least in the absence of light, to its 

 habits. 



It is possible that this case may have some bearing on the 

 general question of the origin of the subterranean fauna. It 

 has been stated, more especially with regard to the Crustacea^ 

 that the subterranean forms are allied, not to the surface- 

 living freshwater species, but to marine and, in some cases, 

 deep-sea forms. Some of the cases formerly adduced in 

 support of this view have been disposed of by subsequent 

 criticism *, but a few forms still remain which appear to be 

 distinctly of a marine type. Among these the Isopod 

 Cruregens, described by Prof. Chilton from wells in New 

 Zealand, belongs to an otherwise exclusively marine family, 

 the Anthuridae. The same may be said of Dr. Benedict's 

 Cirolanides f and the Cirolana eubensis recently described 

 by Mr. Hay J, both belonging to the Cirolanidas, while in 

 some other cases an affinity with freshwater forms seems to 

 have been assumed rather than demonstrated. Among the 

 other groups of subterranean animals the most striking case 

 in point is that of the two fishes Lucifuga suhterraneus and 

 Stygicola dentatus § found in caves in the island of Cuba, 

 to which Mr. Boulenger has kindly directed my attention. 

 These belong to the Brotulidte, a family wiiicli has no other 

 representatives in fresh water, the great majority of the 

 genera coming from deep water, altiiough some are shallow- 

 water or shore fishes. The nearest allies of the cave-fishes 

 are stated to be the genera Brotula and Ogilbia from shallow 

 water and Bassozetus and Aphyonus from 1000-2000 

 fathoms ||. 



In all these cases the cave-dwelling animals, though living 



/ in fresh water, are probably descended from forms which 



have penetrated into the reservoirs of subterranean water by 



of the abyssal plankton are sometimes brought to the surface by the 

 strong tidal currents in the neighbourhood of the Canaries (SB. Akad. 

 Wiss. Berlin, 1889, (2) p. 550). 



* Cf. Chilton, " The Subterranean Crustacea of New Zealand," Trans. 

 Linn. Soc, 2nd ser. Zool. vi. (2) p. 255 (1894). 



t Proc. U.S. Nat. Mus. xviii. p. 015 (1896). 



X Proc. U.S. Nat. Mus. xxvi. p. 430 (1903). 



§ Poey, ' Memorias sobre la Historia Natural de la I^^la de Cuba. . . .,' 

 ii. (1856-1858) pp. 96 & 102, pis. ix. .& x. ; and ' Repertorio tisico-natural 

 de la Isla de Cuba,' i. (1865-186i)) p. 113 ; Gill, Proc. Acad, Philadelphia, 

 p. 252 (1863). 



II See Lane, " The Ovarian Structure of the Blind Fishes Lucifuga and 

 Stygicola;' Biol. Bull. vi. p. 38 (1904). 



