123 



This family contains both Old and New AVorld genera, but most of 

 them belong to North and South America, They are of great interest 

 and have been much studied on account of their many peculiar struct- 

 ures, and because of the deadly effects of their venom. Those who are 

 interested in learning more about the anatomy of these dreadful serpents 

 may consult such works as Huxley's Anatomy of Vertebrates, the various 

 encyclopedias, and volumes XII and XXV^I of the Smithsonian Contri- 

 butions to Knowledge. An interesting popular summary of the results 

 of the studies of Drs. Mitchell and Reichert may be found in the Cen- 

 tury Magazine for August, 1889 (vol. XVI, 503). 



Key to the U. S. Genera of Crotalldce. 



A. Tail not provided with a rattle. Agkistrodon, p. 123. 



AA. Tail provided with a rattle. 



a. Upper surface of head with the usual 9 crown-shields. 



Sistrurus, p. 125. 



aa. Vertical and occipital plates replaced by small scales like 



those of the back. Crotalus, p. 128. 



Genus AGKISTRODON, Beauv. 



Agkistrodon, Pal. de Beauvais, 1799, 36, iv, 381; Baird and Girard,, 

 1853, 6, 17 ; Ancidrodon, of Various authors. 



Head flat, triangular, with 9 crown-shields. Loral present or absent. 

 Scales in 23 to 25 rows, all keeled. Anal plate entire. Subcaudals not 

 divided except some of the posterior. No rattle. 



Loral present. Scales in 23 rows. contortrix, p. 123. 



No loral. Scales in 25 rows. piscivorus. Appendix. 



Agkistrodon contortrix, (Linn.). 

 Copperhead. 



Boa contortrix, Linnaeus, 1766, 64-, ed. xii, 373 ; Trigonocephahis con- 

 toi'trix, Holbrook, 1842, 54-, iii. 39, pi. 8 ; Agkistrodon conti»irix, Baird 

 and Girard, 1853, 6, 17; Ancistrodon contortrix, Garman, 1883, 13, 120, 

 pi. 8, %. 1. 



Head large, flat, triangular, and with the sides in front of the eyes 

 peipeudicular. Neck slender. Tail short, about one-eighth the total 

 length, ending in a curved horn. Vertical plate as broad as long, pen- 

 tagonal. Occipitals about the size of the supercillaries, showing a ten- 

 dency to break up into smaller scales. Both pairs of frontals well 

 developed, extending out to the edge of the upper surface of the head. 

 A small plate sometimes lying between the vertical and the postfrontals. 

 Two anteorbitals, the lower smaller and bounding the pit above. A loral 

 present. Nasal divided, with the nostril present. Rostral broad and 



