958 REPORT OF NATIONAL MUSEUM, 1898. 



south as Vera Cruz from its Xortli American range. In the Old 

 World two species only, T. mortuarius and T. ferox^ are found in 

 Africa, and several species occur in the Malaysian Archipelago. They 

 are all aquatic in their habits, liviug chiefly in and on the shores 

 of fresh waters and feeding on small fishes and other aquatic verte- 

 brates, especially frogs. Some of these species grow to a considerable 

 size, and often present a savage appearance, owing to the small eyes 

 and wide gape of the mouth. Even in these specimens the teeth are 

 not large enough to inflict more than slight and harmless scratches. 



An allied genus accompanies this one in the East Indies (Aniphi- 

 esma Dumeril and Bibron), in which the scales have no pits. In North 

 America another allied genus {Eutcvnia) also has no pits, and is further 

 characterized by the undivided condition of the anal scutum. 



I find twelve well-distinguished species in North America, which are 

 characterized as follows : 



I. Temporal scuta 1-2 or 3; parietal scuta normal. 



a. Oculars 2-2 ; scales in 19 rows. 



Smaller, muzzle wider; three black stripes above; four brown ones below; 



first row of scales keeled .' N. leieris LinnjBUS. 



Larger, muzzle narrower ; no black bands above; two, sometimes three or 



four, imperfect bands below N. grahamii Baird and Girard. 



Muzzle short, brown above, with a broad median band; below yellow, with 



two rows of spots; first row of scales smooth N.rigida Say. 



aa. Oculars 1-2 ; scales in 21 rows. 



Superior labials 8; head elongate ; brownish yellow, immaculate. iY.Msto Cope. 

 aaa. Oculars 1-3; scales in 19-21 rows. 



Four brown bands above ; a median row of yellow spots below. 



iV. clarkii Baird and Girard. 

 Three rows of brown spots above, which may form stripes anteriorly and 

 cross bands posteriorly; a median row of yellow spots below. 



N. compressicauda Kennicott. 

 A row of lateral spots, often indistinct; below uniform; tail slender, cylin- 



dric N. valida Kennicott. 



aaaa. Oculars 1-2-3 ; scales in 23-25 rows. 



Superior labials 9; preoculars 2; spots longitudinal N.Mseeta Cope. 



Superior labials 8 ; jjieoculars 1 ; spots when present transverse. 



K. fasciata Linnaeus. 

 aaaaa. Oculars 1, 2-3, 4; scales in 27-29 rows. 



Eye resting on (usually one) labial; alternating wide dorsal and lateral 



spots connected at angles N. rhomhifera Hallowell 



Eye separated from labials by scales; numerous narrow cross bauds, somi'- 

 times broken N. cijclopiuvi Dumr'ril and Bibron. 



II. Temporal scales 2-4, 5; parietals much reduced in size. 

 a. Oculars 1-2; scales 31-33 rows. 



Eye resting on one labial ; alternating dorsal and lateral spots, which do not 

 touch N. taxispilota Holbrook. 



Of these species N. leheris and ISf. fasciata are distributed over both 

 the Eastern and the Austroriparian districts. The other species belong 

 to the Austroriparian district except the If. valida, which is the only 

 species of the Sonoran district. The N. graliamii extends up the Mis- 

 sissippi River to north of the Austroriparian limits to northern Illinois 

 and Indiana, and is not known from onst of tbo latter State. K. rhom- 



