246 BULLETIlSr 15-1, UNITED STATES NATIONAL MUSEUM 



border of the third siipraociihir in G speciineiis, and to the center 

 of the second supraocular in 5 specimens. The forking of the dorsal 

 stripe varies from 4.5 to 35.4 per cent of its length, includin<:- llic 

 fork. 



Range. — San Jose Island, Gulf of California, Mexico (Van Den- 

 burgh, 1895^, p. 132, C.A.S., M.C.Z.). 



Habitat and habits. — Nothing has been recorded on the habits of 

 this species. San Jose Island is nearly 17 miles long and from 2 to 

 6 miles wide. It is covered in most parts by vegetation, especially 

 on the high land and in the numerous deep arroj^os of its north- 

 eastern portion. In general, its surface is a succession of high rocky 

 bluffs, with a few intervening sandy beaches. 



Acuities. — This little-known lizard is most closely allied to C 

 hyperythrus hyj)eryt/trus, from which it has a])parently been derived 

 in geologically recent times. The transition from hy perytlirus to 

 (lahhciniac may be seen in certain mainland specimens of hypery- 

 thrus that have a low percentage of forking of the anterior portion 

 of a single median dorsal line. In certain of these the unforked 

 portion of this line is intensified and widened in such a way as to 

 very significantly approach the condition found in danheinnae and 

 caerideus. The race-runners of San Francisco Island are geograph- 

 ically intermediate between danheimae and hyperythrus., but are 

 nearer to the latter in characters, although certain of the specimens 

 approach the former by a progressive differential coloration of the 

 sides and back and by the intensification and widening of the dorsal 

 stripe. Therefore, there is really no great break between the two 

 extremes, hyperythrus and danheimae. 



SUMMARY OF THE HYPERYTHRUS GROUP 



The hyperythrus group is confined to the general Lower Cali- 

 fornian region. The resemblances among the various forms of this 

 homogeneous natural unit greatly outweigh the differences, for 

 throughout the series there is a remarkable uniformity in the gen- 

 eral appearance of the body as well as in most other structural fea- 

 tures. All of the forms are relatively small, seldom exceeding a 

 length of over 80 millimeters, and the limbs and tail are slender 

 and weak, giving a general impression of fragility. 



The hy perytlirus group is composed of four forms, a mainland 

 prototype, liypenjthrus., and three island derivatives, caerideus.^ pic- 

 tus, and danJieivuie. Since a consideration of the group as a whole, 

 and hence of the prototypic hyperythrus.^ is to be given in the general 

 summary at the end of this work, the present discussion will be 

 limited to the origin and relationships of the three derivatives. 



