46 ILLINOIS BI OLOGI CAL MONOGRAPHS [46 
branous partition separating the internasal space from the cavum cranii. 
It would follow then, that Diemictylus is probably reduced from some 
form like Triton, and both genera are related to Salamandra which has 
developed along a line parallel to Amblystoma; and it is through some 
Spelerpes-like larva, as far as the nasal capsules are concerned, that 
Salamandra, Triton and Diemictylus are related to the group including 
Plethodon and Amblystoma. 
Necturus and Proteus have often been regarded as primitive and Cope 
(1889) included them in a group, Proteida, apart from the Urodeles, 
although ancestral to them. I have not examined Proteus, but upon the 
basis of the nasal capsule of Necturus, which cannot be regarded as ances- 
tral, Cope’s position can not be affirmed. Pinkus (1894) called attention 
to the similarity of the nasal capsules of Necturus and Protopterus, a 
similarity based wholly upon the fenestration of the capsules, and not upon 
structural resemblances. The parts of the capsule of Necturus may be 
homologized with those of other Urodeles, but many differences have arisen 
in the appearance of these parts, so that relationships are very remote. 
Many parts of the capsule chondrify independently, later uniting to each 
other; the ethmoidal column, however, never unites to the other parts of 
the capsule, but by lateral growths produces the fenestrated roof over the 
nasal sac. Necturus is greatly retarded in the development of its nasal 
structures. Ina 25 mm. larva only trabeculae are present, there being no 
evidence of cornua or planum basale or columnae, as in corresponding ages 
of Amblystoma and Salamandra. The earlier larvae of Spelerpes, Des- 
mognathus, and Necturus seem to resemble each other very closely in their 
cylindrical trabeculae, slight cornual expansions and absence of trabecular 
crests. In the later stages, however, further resemblance is lost, for 
Spelerpes has gained true Urodelan characters while Necturus still possesses 
larval relationships; a fact, which, together with the retarded process of 
chondrification, suggests for Necturus that it may be a persistent larva, as 
has often been suggested. 
As stated above, Cope placed Proteus with Necturus in the Proteida, 
regarding them as primitive Amphibia, and related to the Stegocephala by 
the presence of an intercalary bone. Kingsbury (1905) rejects Cope’s 
thesis, affirming the absence of an os intercalare in Necturus, and suggested 
that Cope had probably regarded the posterior process of the opisthotic 
as an intercalary; furthermore he regards the intercalary of the Stegoce- 
phala as a membrane bone. 
Norris (1911) working on the cranial nerves of Necturus, concludes 
that it cannot be regarded as primitive. The distribution of the cranial 
nerves agrees in detail with that of the higher Urodeles, a condition which 
would not be expected in a primitive form. Kingsbury, like others, has 
regarded Necturus as a neotenic larva, and would place it near Spelerpes. 
