CAVE FISHES OF NOKTH AMERICA. 391 



TROGLICHTHYS Eigenmann. 



Trofjlkhthys Eigenmann, Science, "N. S., IX, 1899, 280 {rosve). 



This genus is veiy much like TyphJichthys^ from which it differs in 

 the structure of the 63^68, especial Ij^ by the presence of large scleral 

 cartilages. 



Trogliclithys rosse (Eigenmann). PL IV, fig. 1. 



Body similar to that of TyjMlchthys, but sliglitl}' heavier. Depth 

 4.5 in head; head 3, depressed; mouth oblique, lower jaw slightly pro- 

 jecting; snout rounded; eye not visible, considerably smaller than that 

 of Typhi icJithys; gill membranes joined to isthmus; head and hodj 

 well supplied with tactile ridges; tins similar to those of Typlillchthy8\ 

 dorsal with 8 rays; anal 8; pyloric coeca 2. Color in life, yellowish 

 pink, no dark spots an^nvhere. Length 1.167 in. 



T, rosx inhabits subterranean waters in southern Missouri, north- 

 ern Arkansas, and probably eastern Kansas. The type specimens are 

 from the caves at Sarcoxie, Mo. It is this species whose habits Doctor 

 Garman and Miss Hoppin have studied. 



The following is quoted from Doctor Eigenmann in Science, N. S., 

 IX, 1889, 280. "On the surface the specimens very closely resemble 

 Typlil'icldhys suhterraneus from the Mammoth Cave. * * * It is, 

 however, quite evident from a study of their eyes that we have to deal 

 here with a case of convergence of two distinct forms. They have 

 converged l:>ecause of the similarity' of their environment, and especially 

 owing to the absence of those elements in their environment that lead 

 to internal protective adaptation. * * * The eye of TypldicJithys 

 is surrounded by a very thin layer of tissue representing the sclera 

 and choroid. The two layers are not separable. In this respect it 

 approaches the condition in the epiga?an-eyed member of the family, 

 Chologaster. The eye of Troglickthys 7'osse is but about one-third the 

 diameter of that of Typhlichthys subterraneits, measuring 0.06 mm. or 

 thereabouts. It is the most degenerate, as distinguished from the 

 undeveloped vertebrate eye. The point of importance * * ^' is the 

 presence of comparatively enormous scleral cartilages. * * * This 

 species is unquestionably descended from a species with well-developed 

 scleral cartilages, for it is not conceivable that the sclera as found in 

 Chologaster could, by any freak or clmnee, give rise during degenera- 

 tion to scleral cartilages, and if they did they would not have devel- 

 oped several sizes too large for the eye. At present no known epigtean 

 species of the Aniblyopsidse possesses sclei'al cartilages and the ej^e of 

 rossn passes thi-ough a condition similar to that possessed by AmNyop- 

 sis, but the latter species has ventral fins, and is hence ruled out as a 

 possible ancestor of rosse. * * * Judging from the degree of degen- 

 eration of the eye, Trogliclitliys has lived in caves and done without 

 the use of its eyes longer than any other known vertebrate." 



