170 MAJOR F. WALL, I.M.S., O.M.Z.S. 



teeth, a point of material importance in the present accepted classification. Where 

 my observations differ from Mr. Boulenger's, I can only explain the discrepancy on 

 the supposition that my vision may be keener than his, and the lens I worked with of 

 higher power. Certain it is that grooves which were invisible under the lens I had 

 previously used under the assurance that it was the strongest made, became clearly 

 revealed by a new lens of the very highest power and quality specially recommended 

 me for this work by Messrs. Baker, opticians, Holborn. More recently inspection with 

 the aid of the microscope has confirmed my observations with this pocket lens. 



Mr. Boulenger records the occurrence of solid posterior maxillary teeth in the 

 genera Hydrus, Acalyptus, Hydrelaps, Enhydrina, Platurus and Hydrophis (in all of which, 

 however, I can discern grooves). So far as the first five are concerned, this point does 

 not influence his classification, but the genera Hydrophis and Distira are divided solely 

 on the assumption that the small teeth are solid in Hydrophis , grooved in Distira. Now 

 I find that in Hydrophis the small teeth are all grooved (not solid as Mr. Boulenger 

 states), and being so, conform to the condition he claims to characterise the genus 

 Distira. The error is one easy to understand, for many of his species of Hydrophis are 

 snakes with very small constricted heads, and some of them, even when adult, are of 

 notably small proportions. I could find no specimen for instance, of H. gracilis in 

 the British Museum collection that enabled me to clear up this point, but in the Colombo 

 Museum I saw three well-grown adults in which the grooves were plainly visible. 

 In this connection I may point out that Mr. Boulenger in the lc Fauna of British India 

 Reptiles and Batrachia," published in 1892, says that the small maxillary teeth behind 

 the fangs in the genera Naia and Bungarus are solid, but recognises and corrects these 

 mistakes four years later in his Catalogue, Vol. Ill, pp 373 and 365, where he rightly 

 pronounces them grooved. This question of grooves has led to much confusion, for 

 Mr. Boulenger has, in many cases, been led to describe as a new Distira a well-grown 

 specimen of some previously known species of Hydrophis , the grooves well marked in 

 the large adult snake having escaped detection in smaller or less perfect specimens. 

 I have failed to discover a single species in the whole of the sub-family Hydrophiince 

 with the posterior maxillary teeth ungrooved. 



Some remarks upon the external characters concerning classification are, I think, 

 called for, and in deahng with these I shall refer to them in what I consider their order 

 of relative importance beginning with the ventrals. 



Ventrals. — The presence or absence of these shields, and their development 

 especially as regards breadth, are of the greatest importance in the separation of genera 

 and species. They are absent in Astrotia stokesi being replaced by scales but little 

 modified from those of the adjacent costal rows (see fig. 65 D). They are so ill- 

 developed in the genus Enhydris that, except anteriorly in E. curtus, they might be 

 better considered absent (see fig. 63). They are barely as broad as the last costal row 

 in Hydrus, Acalyptus and Thalassophis. In Hydrelaps, Enhydrina and Distira they 

 are rather less than twice the last costal row (see fig. 38). In Distira viperina they are 

 unique, the anterior shields being three or four times as broad as the last costal row, the 



