156 VERTEBRATE ANIMALS OF THE UNITED STATES 



atrophy in the young and grow again in the adult; i or 3 pairs of gill 

 slits; eyes very small; 2 patches of teeth on prevomer; premaxillaries 

 and mandibles toothless and with horny sheaths: 2 genera and species. 



Key to the Genera of Sirenidae 



ai Leg with 4 toes i. Siren. 



an Leg with 3 toes 2. Psendobranchus. 



1. Siren L. Four toes on each leg; 3 pairs of gill-slits present: i 

 species. 



S. lacertina L. Mud eel. Body dark gray above, lighter beneath, 

 more or less cylindrical in shape; head flattened; snout truncate; tail 

 compressed; lateral grooves 31 to 37; length 700 mm.; tail 240 mrn.; 

 fore leg 38 mm. : south Atlantic and Gulf States, from District of 

 Columbia and central North Carolina to the Rio Grande, and north- 

 wards in the valley of the Mississippi to Alton, Illinois and Lafayette, 

 Indiana; in swamps; often common. 



2. Pseudobranchus Gray. Three toes on each leg; i pair of gill 

 slits: I species. 



P. striatus (LeConte). Body light with dark stripes; snout pointed; 

 mouth very small; length 150 mm.; tail 65 mm.; fore leg 4 mm.; gills 

 often covered by a fold of skin: South Carolina to Florida; in swamps; 

 not common. 



Order 2. Salientia {Anura). — Frogs and toads. Amphibians 

 with two pairs of well developed legs and without a tail in the adult 

 stage, but with a long tail and weak legs during some stage of the larval 

 life (American forms). The body is short and compact, there being in 

 most cases nine vertebrae, and either no ribs or three very short ones; in 

 addition to the vertebrae is the urostyle, a bone which is homologous to 

 the caudal vertebrae and extends backward from the pelvic girdle. The 

 hind legs are usually long and muscular. The head is generally very 

 large; the eyes are large and protruding, and the eyelids well developed; 

 the tympanum is flush with the surface of the skin. Just behind the eye 

 and behind and above the tympanum in the toads is a conspicuous 

 raised glandular area called the parotoid gland (Fig. 81). The general 

 surface of the skin is glandular, and is either smooth or tubercular and 

 warty. The color is often bright, and metachrosis is very general. 

 The male, in most forms, has a large vocal sack which opens into the 

 mouth by one or two slits in its floor, by means of which it can produce 

 a call which is often very loud; they can, however, croak without the aid 

 of their vocal sacks, and some species do not have them. The tongus 

 is absent in the tropical family Fipidce, but in most of the others it ie 



