218 G. A. BouLENGER, On some tree-frogs allied to Hyla caerulea. 
which is enlarged and bent inwards, and a smaller one on the basal 
phalanx; the sharply pointed conical spines with which they are 
studded are so large that they can be distinguished with the naked 
eye. In H. caerulea and H. infrafrenata, the black nuptial rugosities 
consist of isolated small spines crowded together in one or two patches 
as in our Rana temporaria. As in H. caerulea, the omosternum is 
quite normal, cartilaginous. 
It is very remarkable indeed to find two species so closely related 
as H. infrafrenata and H. humeralis diftering so strikingly in the 
characters connected with the nuptial embrace, although we are not 
unprepared for such diserepancies. The late Prof. BoETTGER has des- 
cribed !) a small tree-frog from Costa Rica, Hyla prosoblepon, in which 
a sword-shaped bony process is present on the inner side of the arm. 
Another species, from Bolivia, named by me Ayla armata?), bears three 
large black, horny, pluricuspid nuptial plates, one under the arm, two 
close together on the inner side of the inner finger. "The use of these 
plates is evidently for the male to clasp more securely the female 
during the breeding operations, but the way in which the plates on 
the fingers are exactly opposed to that on the arm suggests the 
possibility of their being also stridulating organs. In the male of 
Oauphias guatemalensis BRoccHL?), the rudimentary pollex terminates 
in a very sharp spine at right angle to the inner digit. Among the 
secondary sexual characters in the Hylidae, the ldrge flat gland on the 
side ofthe male Ayla rosenbergiüi BLer.*) deserves mention as analogous 
to the humeral gland of Pelobates, the function of which in still unex 
plained. Asa general rule, nuptial or copulatory horny exerescences 
are absent or very feebly developed in the Hylidae, although there 
are exceptions, as in the South American Hyla leprieuri, which may 
even possess them under the toes; and again, closely allied species 
may show much difference in this respect, as for instance Hyla arborea 
and MH. chinensis. It is however worthy of note that, whilst brown 
or black horny rugosities are rather the exception in the American 
forms (only about a dozen S. American Hylidae, Phyllomedusa, Driprion, 
being provided with them), their presence is the rule in the species 
of Hyla and Hyllella inhabiting Australia and Papuasia. 
1) Kat. Batr. Senckenb. Ges., 1892, p. 45. — It is through an over- 
sight that I ascribed the character in question to another tree-frog from Costa 
Rica, HAylella fleischmanni BOETTG., in: Les Batraciens (Paris 1910), p. 165. 
2) Ann. Mag. Nat. Hist. (7), Vol. 10, 1906, p. 294. 
3) Mission Scient. au Mexique, Batraciens, p. 63, pl. 12, fig. 3 (1882). 
4) Proc. Zool. Soc., 1898, p. 123, pl. 16. 
