170' 



eropygii, as we have for their mutability and late develop- 

 ment, and to one of my, perhaps, too deeply rooted ideas, 

 a far more satisfactory theory ; for, with our present 

 knowledge, it is but theory on either side. 



The following synopsis gives a summary of the charac- 

 ters of the family, genera and species. 



HETEROPYGII TELLKAMPF, Muller's Arch. f. Anat., p. 392, 

 1844 ; and New York Journal of Medicine, v, p. 84, 1845. 



Jfypsceidce Storer, Synopsis X. A. Fish, p. 435, 1846. 



Brain of ordinary development in all its parts, similar to that of 

 Cyprinodontes and of about the same proportions. Cerebral lobes 

 larger than the nearly round optic lobes. Cerebellum overlapping the 

 posterior third of the optic lobes. Medulla oblongata broad, with 

 well defined right and left sides. (On comparing the brains of the 

 three genera the only difference noticed was that in Chologaster the 

 cerebellum was not quite as large proportionally, but more elongated 

 and not quite as wide as in the other genera, while the optic lobes of 

 this genus with well developed eyes were no larger than in a Typh- 

 lichthys of the same size.) 



Skeleton not studied. Giinther gives the vertebrae as thirteen ab- 

 dominal and nineteen or twenty caudal. The bones of the head are 

 thin and mostly flattened as in the Cypriuodontes. Occiput slightly 

 convex. jp 



Body compressed posteriorly. Head and anterior portion of body 

 depressed, giving the form of a broad, flat head, with a compressed 

 tail. 



Branchiostegal rays six in number and but slightly covered by oper- 

 cular bones ; opercular opening large. 



Fins. Dorsal and anal nearly opposite and posterior to centre of 

 body. All the fins except the ventrals well developed, with central 

 rays longest and first rays simple. Pectorals close to the head, about 

 in the middle of the sides. (Ventrals present in Amblyopsis, absent 

 in Typhlichthys and Chologaster.) 



Mouth opening upwards, with lower jaw slightly projecting. Mar- 

 gin of the upper jaw formed by the intermaxillaries. Maxillaries 

 placed behind the intermaxillaries, with lower third broad amd below 

 the intermaxillaries. Several rows of fine teeth on the intermaxil- 

 laries and lower jaw. (Teeth on palatines in Amblyopsis and Typh- 

 lichthys, noue on these bones in adults of Chologaster.) 



