NATURAL SCIENCES OF PHILADELPHIA. 303 



II. Prefrontal and nasal plates distinct ; dentition isodont. 



a. Loreal absent. 



Scales uniporous ; vertical produced anteriorly ; one nasal, Toluca. 



b. Loreal present. 



One nasal, two postoculars ; rostral much depressed, Chionactis. 



Two nasals, three postoculars : rostral little depressed, Sonora. 



Gyalopium and Amblymetopon form another group, characterized by a 

 stout form, distinct head, and iecurved rostral shield ; size small. 



Chilomeniscus c i n c t u s Cope. 



Rostral plate projecting far backward, entirely separating the prefrontals, 

 encroaching upon the postfrontals ; the latter are in contact with the labials. 

 Nostril counected by suture with the fronto-nasal suture. One very small 

 preocular, two postoculars. Seven superior labials, the first longitudinal, the 

 remainder vertical except the last two, which are nearly equilateral. Sym- 

 physeal in contact with geneials. Scales broad, very smooth, in thirteen rows. 

 Tail very short. Gastrosteges 11, one divided anal ; urosteges 21 pair. Total 

 length seven inches, tail eight lines. Ground color white, with a reddish 

 tinge, encircled by sixteen black rings upon the body, and three upon the tail. 

 There are four or five scales in width, and separated by equal spaces ; they 

 are narrower on the belly. The head is black from the extremities of the oc- 

 cipital plates to the anterior part of the vertical, and to the second labial 

 plate. Chin shaded with black. 



Habitat. Near Guaymas, east coast Gulf of California. Mus. Compar. Zo- 

 ology Cambridge, No. 24. 



The coloration is that of the species of Chionactis. 



Stenorhina-1 a c t e a Cope. 



Similar in most respects to S. v e n t r a 1 i s. Tail one-seventh of the total 

 length. Scales in seventeen rows. Occipital shields longer than in S. v e n- 

 tr ali s, their common suture much longer than their supercilio-ocular. Ver- 

 tical more elongate, with shorter latero-posterior borders. Frontals broader, 

 (longitudinally) ; rostral plate more prominent. Postnasal in contact with 

 preocular by a very short suture. Seven superior labials, broader than in S. 

 ventralis. Six inferior labials, the first homologically equal the first and 

 second. Preanal shield divided. 



Total length 25 inches 5 lines ; tail 3 inches 7 lines. 



Color above brownish white ; beneath paler. An indistinct band passes 

 through the temple and eye to the muzzle. 



Habitat. Guatemala. Specimen 4944. from La Union, Capt. Jno. M. Dow's 

 oil. 



Stenorhina ventralis Dum., Bibr., Cope, Pr. A. N. S. 1860, 242. 



A common serpent near Mirador, Vera Cruz, as proven by Dr. Sartorius. In 

 this species the scales are uniformly poreless ; in S. 1 a c t e a a single pore is 

 rarely seen ; in k e n n i c o 1 1 i a n a (I.e. 242) a regular pair of pores, one 

 odd, or one median pore, are sometimes observable. 



Boa e q u e s Eyd. et Souly. 



Capt. J. M. Dow has sent this species from Guatemala to the Academy ; an- 

 other specimen in the same collection is said to have come from Caraccas. 

 Greytown, Nicaragua, is a locality whence it has been sent to the Smithsonian 

 Institution. 



The scales of the orbital ring do not always rest upon the superior labials. 

 The species is, however, easily recognized by its stout form, approximate spots, 

 short, elevated muzzle, and general dark color. The rostral plate is always 

 more constricted at the base than in B. constrictor, the labials less nu- 

 merous and more elevated. 



1861.] 



