214 Proceedings of the Biological Society of Washington. 



of the first three rows. These take the form of light bars four or five dorsal 

 scale lengths apart. The scale which has the light spot also has a dark tip. 

 On the tail these narrow cross bars extend to the mid-dorsal line. There 

 are four such light bars on the tail, the posterior third of which is uniform 

 and darker than the color elsewhere. The belly is very finely punctulated 

 with light and dark. Head above same as body, an indistinct light band 

 from eye to angle of jaw including the last four upper labials and extending 

 more or less continuously though faintly above the edges of the ventrals 

 through the anterior half of the body. Throat dark, last six lower labials 

 with a vertical white bar. 



Dimensions. — Length, 370 mm. ; tail, 46 mm. 



Remarks. — This snake merits comparison with L. godmani and L. aurifer 

 rather than with any Lachesis hitherto recorded from Mexico (i. e., lanceo- 

 latus, nummifer, lansbergii, brachystoma and undulatus) . It has a lower scale 

 count than any American species. 



With aurifer (the next lowest, with 19 scale rows) it is allied by the en- 

 larged frontal and the ventral count. But it differs in the smaller number 

 of subcaudals, in the two less scale rows, in the greater number of oculars, 

 and in some being in contact with the labials, in the divided nasal, in the 

 labials being occluded from the pit, and in coloration. 



With godmani there is close agreement in coloration save in the peculiar 

 throat of the new form, the subcaudal count is the same. Godmani some- 

 times has the enlarged frontal separated by one row of scales from the 

 supraocular, the labials do not enter the pit, and the nasal is divided. But 

 here the resemblance ends for godmani has 21 scale rows, a much lower ven- 

 tral count, a more acute canthus rostralis and the suboculars are cut off 

 from the labials. 



It would seem that barbouri is a link between godmani and aurifer showing 

 characters of both and being more primitive than either in head scalation 

 and having (dwarfing due to altitude?) a lower number of dorsal scale rows 

 than either. 



It is interesting to note that godmani and aurifer are usually put in differ- 

 ent sections of the genus because of the possession of a prehensile tail by 

 aurifer, and these sections have been elevated at times to generic rank. 

 Bothriechis Peters 1859, type B. nigroviridis Peters, for the arboreal, pre- 

 hensile tailed forms; and Bothriopsis Peters 1861, type B. quadriscutatus 

 Peters (=castelnaudi D &B fide Boulenger etCope), for the terrestrial, non- 

 prehensile tailed forms. 



I do not believe that these divisions can be maintained on this character. 

 Bothriechis is therefore the generic name for the American Lachesis with 

 undivided subcaudals in case they are thought not congeneric with L. mutus 

 and L. atrox. 



Crotalus stejnegeri, sp. nov. 



Diagnosis. — A small Crotalus with a long slender tail, a very small rattle 

 and with the first pair of lower labials long and produced backwards broadly 

 in contact behind the symphysial. 



