EXTERNAL FEATURES AND VARIETIES 13 



MacBride, Knoblauch and others given in the bibliography should 

 therefore be consulted by those interested in this subject. 



VARIETIES 



In spite of so much variation in the relative proportions of the 

 yellow and black pigments, three main and fairly constant varieties 

 stand out clearly. They are based on differences of pattern, and 

 appear to be correlated, to a very large extent, with geographical 

 distribution. These varieties have been carefully investigated by 

 E. G. Boulenger (191 1) and the following description is a resume 

 of his work (cf. Frontispiece). 



1. Forma Typica. 



The first of these varieties may be called the forma typica, since it 

 is the type on which Laurenti first established the genus. In this 

 variety the black pigment nearly always predominates over the yel- 

 low, while the latter pigment is disposed over the body as markings 

 of various shapes, often in three or five alternating series, or with 

 a median series forming a sinuous or zigzag vertebral stripe. Very 

 exceptionally the dorsal markings may appear to form two longi- 

 tudinal series, but in such a case they never hang together in regular 

 chains continuous with the spots on the paratoids. The upper eyelids 

 and paratoids are usually entirely, but sometimes only partially, 

 yellow, and these usually remain distinct from each other, but they 

 may fuse. A yellow spot occurs nearly constantly above the angle 

 of the mouth, while the snout is usually entirely black. There are 

 sometimes a few markings in the gular region, but they may be 

 absent. The ventral surface is either quite black or marked by a few 

 small spots. The limbs are black with a characteristic and constant 

 yellow patch on the proximal portion of the dorsal surface of the 

 arm and thigh, and a second similar patch may or may not occur 

 on the distal portions of the limbs. The spots on the tail may be 

 single or paired, or they may form a stripe. The ventral surface of 

 the tail is nearly always black. The colour of the markings varies 

 from chrome-yellow to deep orange. 



With very few exceptions all specimens occurring to the east and 

 south of a line drawn through the Erz mountains, the Danube, the 

 Alps, and the Rhone belong to this form (PL XXV, fig. 84). 



2. Variety Molleri. 



The second form occurs in the Spanish peninsula. It is the 

 variety molleri of Bedriaga (i 896), and includes Seoane's var. galliaca 



