170 MAJOR F. WALL, LM.S., C.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 asthe first five are concerned, this point does 
not influence his classification, but the genera Hydrophis and Distiva are divided solely 
on the assumption that the small teeth are solid in Hydrophis, grooved in Distiva. 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 
Distiva. The error is one easy to understand, for many of his species of Hydvophis 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 ‘‘ 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. III, 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 Distiva a well-grown 
specimen of some previously known species of Hydvophis, 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 Hydrophiine 
with the posterior maxillary teeth ungrooved. 
Some remarks upon the external characters concerning classification are, I think, 
called for, and in dea'ing 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 asthe last costal row 
in Hydrus, Acalyptus and Thalassophis. In Hydrelaps, Enhydrina and Distiva they 
are rather less than twice the last costal row (see fig. 38). In Distiva viperina they are 
unique, the anterior shields being three or four times as broad as the last costal row, the 
