200 On a new Genus of Clawless Otter. 
ships of the three genera of clawless otters now known; in 
the course of their evolution they seem to have followed paths 
in part parallel and in part divergent. It is still more difficult 
to decide whether Paraonyx, Aonya, and Micraonyz, together 
with the extinct Enhydriodon and the living Latax, are 
retrograde developments from active fish-catching ancestors 
rather than the terminations of so many progressive lines 
leading from forms at least as generalized as the Tertiary 
Potamotherium. Forsyth Major (Zool. Anz. 1897, p.138) sees 
in Aonyx, Micraonyx, and Enhydriodon “ phylogenetisch 
iltere Formen”; but Winge (‘ Rovdyr fra Lagoa Santa,’ 
1895, p. 69) suggests a retrograde development from forms 
resembling Lutra. Personally I incline to the latter view as 
regards the clawless otters ; for in the broader details of their 
structure they are all as much otters as is Lutra itself, and 
it is difficult to account for such essential agreement except 
upon the supposition that the three clawless genera have 
passed through similar free-swimming fish-catching stages of 
development. The differences between them and Lutra are 
correlated apparently with slight differences of habit and 
environment; while forming strong pegs for the systematist 
to hang his elassification of numerous forms upon, these 
differences are in themselves small things of possibly little 
basic significance. One point in this connection may be 
specially mentioned. In Potamothertum and Lutra, as in 
many other carnivores, 24 and “1 are only in contact by 
their external angles, a large space is left vacant between 
them lingually; into that interdental space bite the two 
chief cusps (4 and 2 of Winge’s numeration) of the lower 
carnassial. In the three clawless genera, as well as in 
Enhydriodon and Lataa, *-* and ™-1 are in full contact, and 
there is no lingual interdental space ; the inner lobes of the 
upper teeth are so greatly developed that all the cusps of aq 
bite on to hard tooth instead of on to soft gum—an obvious 
adaptation, be it progressive or retrogressive, for crushing the 
shells of molluscs and crustaceans. This adaptation is clearly 
much older and more perfect in Latax than in any clawless 
otter ; and therefore it is not surprising to find the characters 
of #4 and ™! not merely foreshadowed but practically 
perfected in their representatives of the milk-dentition @:8 and 
@-4 (figured by Leche, Zool. Jahrb. 1915, p. 342). But in 
Aonyx avd Micraonyx %#-3 and 4-4 are totally different from 
their permanent representatives in form, showing a wide 
lingual interspace, which receives the chief cusps of #4; the 
milk-dentition in these forms still remains faithful to the type 
exhibited by the Tertiary Potamotherium. 
