310 BULLETIN 34, UNITED STATES NATIONAL MUSEUM. 



fontauelle aud with complete ethmoid arch, and a styloid osseous xiphi- 

 steruum, with terminal cartilaginous disk 5 the auditory organs perfectly 

 developed ; the lowest, undeveloped ethmoid arch and frontoparietal 

 roof, and disciform cartilaginous xiphisternum without style, with 

 Eustachian tubes and membranuin tympani wanting. Accompanying 

 this succession, we have four modifications of the family structure to 

 adapt to as many modes of life: the aquatic, the terrestrial, the arbo- 

 real, and the subterranean. As the earth's surface is the common 

 niedium between the above extremes, so the species of terrestrial habits 

 furnish us with none of the adaptive extremes of structure, but remain 

 an intermediate grouj), from which the succession of structures, inter- 

 rupted, it is true, passes towards the divergent types. Developmental 

 structures accompany and confirm the adaptive, but by no means al- 

 ways coincide. 



The aquatic habit is attained when the digits behind are not only 

 webbed, but when the external metatarsi are separated by membrane 

 also; the arboreal, when the terminal phalanges are furnished with a 

 terminal transverse limb, which supports an adhesive disk. The sub- 

 terranean is shortened, and furnished with a great development of the 

 first digit or prepollex of the tarsus, which is covered b^'^ a corneous 

 sheath, and serves as a spade. The first type may be combined with 

 the third, as in Mixophyes and Chiroleptes, or either may be furnished 

 with a bony overroofing of the temporal muscles, and penetration of its 

 integuments by the hyperossification of the cranium. 



The fossorial spur is weak in Helioporus and Paludicola, weaker in 

 Mitrolysis, and just represented in Ceratophrys. The palmate foot is 

 diminished in Calyptocephalus, reduced in Mixophyes and Chiroleptes, 

 and represented by a trace in Hylorhina and Limnomedusa. The un- 

 developed ear is seen in Telmatobius and in Alsodes. 



The variations in the development of the thumb are not so striking 

 as in the Hylidie. In Gnathophysa, Cystignathus, and Ceratophrys 

 the trapezium supports an osseous metacarpal and obtuse phalange, 

 which are concealed in a large tubercle. In Mixophyes, on the other 

 hand, the metacarpal is slender, entirely cartilaginous, and does not 

 support a phalange. There is nowhere a spur, as in Hypsiboas. 



With regard to the dermal attachments, the following imj)ortant 

 varieties occur; in thefamil}^ generallj^, but especially among Hylodes 

 and Cystignathi, the dorsolateral septum is placed especially high up : 



Fseudes. — Septa in Pseudis as in Eana; in Lysapus the lateroventral 

 line is a little widened. In Mixophyes fasciolatus the lateroventrals 

 are very wide, and leave the ventral free space very narrow behind the 

 middle. 



Ceratophrydes. — In Ceratophrys the lateral septa are narrow, and 

 there are two posterior abdominal transverse septa, similar to those 

 attached to the sternum. In Ceratophrys ornata these are wanting, but 

 the dorsolateral line is very broad. 



