38 ILLINOIS BIOLOGICAL MONOGRAPHS [38 



lamina externa bears a short posterior process from its ventral margin, a 

 remnant of resorption now going on, so that the choanal gap in this stage 

 is incomplete. 



Just in front of the connection of the lower margin of the lamina externa 

 to the cornu trabeculae, the lamina continues forward as two cartilage 

 bars, the upper more cylindrical, the lower somewhat flattened, between 

 which the organ of Jacobson is included. By the fusion of these parallel 

 rods with the alary process above described, an elongate naris is formed 

 which extends over one-half the entire length of the capsule; and at the 

 same time these cartilages all unite to form the tip of the capsule, a flat- 

 tened plate which covers the end of the nasal sac (Figs. 67, 68). 



The nasal capsule of Epicrium is considerably different from that of 

 any other Amphibian and can hardly be said to be Urodelan. In a very 

 few points, resemblances can be drawn between the Caecilian and Urodelan 

 structures; but these are so few, and the modification of the parts in the 

 Caecilian is so great, that few close relationships can be established. The 

 independence of alisphenoid cartilage and trabecula in Epicrium, find no 

 parallel among the Urodela where these parts are continuous and form the 

 wall of the cavum cranii; while in no other capsule do we find the deep 

 and narrow external naris, as is present in my older stage. 



The floor of the capsule is formed by a cartilage called by Peter (1898) 

 the solum nasale, which can be none other than a modified cornu trabeculae 

 which has developed laterally and has united to the lamina externa, just 

 anterior to its fusion with the antorbital process. So that in this relation 

 of cornu trabeculae, lamina externa and processus antorbitalis, there is a 

 condition quite similar to the other capsules, such as Triton and Ambly- 

 stoma, although superficial resemblances are lost. That the solum nasale 

 was a cornu could not be derived from a study of the later stage where 

 the greater development has taken place anteriorly, placing the solum in 

 line with the planum basale; but the resemblance between the cornu 

 trabeculae of my two weeks Cryptobranchus larva and this structure in 

 my younger Epicrium seems to indicate the identity of these parts. 



Superficially, the capsule of Epicrium resembles that of Amphiuma 

 more than any other Urodele. In both the sensory parts are but poorly 

 protected, wide gaps occurring in all sides of the skeleton. The presence 

 of a six-sided planum basale, with its anterior prolongations, the planum 

 verticale with its antero-lateral alary processes are structural resemblances 

 between these animals. On the other hand Epicrium lacks the circum- 

 narial ring of Amphiuma, and in its place has developed a partial cupola, 

 possibly in correlation with the burrowing habit of this Amphibian. 



In the origin of the planum verticale from the basale, as well as in the 

 similarity of their cornua, Epicrium recalls Cryptobranchus; and it does 

 not violate probability to assume that the small process developed 



