A MONOGRAPH OF THE SEA-SNAKES (HYDROPHIIN&). 173 



cens, and tor quota, and very small in Thalassophis annandalei. With rare exceptions 

 the costals are of equal or sub-equal size in the whole body length. In the genus 

 Enhydris, however, there is a notable enlargement of the three or four rows near the 

 ventral median line. This point is not very well brought out in figure 63, which is 

 intended to show the imperfect ventrals. In Emydocephalus ijimce some vertebrals 

 are much enlarged, but even in this species this is not a constant feature throughout 

 the same individual, nor in different individuals. 



Shape. — As a general rule the costals are rhomboidal when imbricate, more or 

 less hexagonal where juxtaposed. The edges of the scales are peculiar in one species 

 especially, viz., Astrotia stokesi, where in the lowest rows they are irregularly dentate, 

 and the apices emarginate (see fig. 66 D). 



Carination. — In many genera the costals are quite smooth as in Platurus, Emydo- 

 cephalus and Aipysurus, but in other genera they are furnished with short, median 

 keels or tubercles to which many authors have attached considerable importance. 

 Personalty I do not share their views. Much attention to this character leads me to 

 think little if any weight can be attached to it, either in the separation of genera or 

 species. I find the degree to which these tubercles are developed varies very much in 

 individuals from birth to maturity, and in individuals of the same species of similar 

 growth. It is not unusual to see young specimens with these tubercles so little in 

 evidence that the scales feel smooth, or almost smooth to the touch, and to meet with 

 old examples which are very rough to the touch. Some authors are inclined to think 

 the degree of development dependent upon the sexes, the males especially showing 

 more pronounced tuberculation. In the case of Enhydris curtus, I have seen speci- 

 mens in which the lowest and enlarged costal rows have the tubercles modified, so as to 

 form spines resembling in size and shape the teats of some small mammals like the 

 guinea-pig. Mr. Boulenger believes this occurs in males (Catalogue, Vol. iii, page 

 300), but my notes on this point are too imperfect to criticise this, or the belief enter- 

 tained by others that males are more strongly tuberculate than others. In many 

 species the scales are bi-, tri- or pluri- tuberculate or spinose, but I cannot see in this 

 condition any means of assisting the classification of genera or species. 



Head Shields. — The actual presence in their entirety of many of these shields 

 is of great importance in the separation of genera and species, but the relationship of 

 these shields is of far less importance, and very secondary to most characters which 

 affect the ventrals and costals. I find that the relationship of many of those shields 

 which preserve the greatest degree of constancy in individuals, and which one must 

 employ in the separation of species, is open to some variation in certain of these 

 species, and it is therefore impossible to lay down hard-and-fast rules regarding head 

 shields for distinguishing the various forms. A very open mind must be kept to prevent 

 creating new species on insufficient grounds. 



I find these shields in most, if not in all, species very prone to become rough and 

 granular with age. In the young they are usually quite smooth, and often glossy, but 

 in very old specimens the asperities are sometimes very pronounced. A good example 



