CAVE FISHES OF NORTH AMERICA. 391 



TROGIilCHTHYS Eigenmann. 



Troglichthys Eigenmann, Science, "N. S., IX, 1899, 280 (rosce). 



This g-eniis is very much like Typhlichthys^ from which it differs in 

 the structure of the ej^es, especially by the presence of larg-e scleral 

 cartilages. 



Troglich.thys rosae (Eigenmann). PL lY, fig. 1. 



Body similar to that of Typhi id dhys^ but slightly heavier. Depth 

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

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

 of TyphlicJithys; gill membranes joined to isthmus; head and body 

 well supplied with tactile ridg-es; fins similar to those of Typlillcldliya', 

 dorsal with 8 rays; anal 8; pyloric c(jeca 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 

 TypJiUcJithys 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 because of the similarity of their environment, and especially 

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

 to internal protective adaptation. * "^" * Tlie eye of Tyj^hlichthys 

 is surrounded by a ver}' thin layer of tissue representing the sclera 

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

 approaches the condition in the epigsean-eyed member of the famih^, 

 Chologaster. The eye of TroglicJithys rosse, is but about one-third the 

 diameter of that of TyphlicJithys suhterraneus, measuring 0,06 mm. or 

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

 undeveloped vertebrate ej^e. 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 cliance, 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 epiggean 

 species of the Aniblyopsldx, possesses sclei-al cartilages and the eye of 

 rosae passes through a condition similar to that possessed by Amhlyop- 

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

 possible ancestor of rosx. * * * Judging from the deg-ree of degen- 

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

 the use of its e3"es longer than any other known vertebrate." 



