A MONOGRAPH OF THE SEA-SNAKES {HYDEOPHIINM). 179 



Distira jerdoni (fig. 58) there are three only, but in all the other forms four are pres- 

 ent excepting Aipysurus australis, where they are too ill developed to deserve the 

 name. 



The first on each side meet behind the mental (except in a few abnormal indi- 

 viduals of a few species) and form a suture, the length of which compared with that 

 between the anterior sublinguals has some importance. In Distira cantoris, D. graci- 

 lis, D. obscura and D. fasciata, etc , this suture is much longer than that between the 

 anterior sublinguals, but in almost all the other species it is little longer and often 

 shorter. The last infralabial is peculiar in Aipysurus eydouxii, Acalyptus peroni, 

 Platuriis schistorhynchus , Distira cantoris, D. gracilis and D. jerdoni, in that it touches 

 but two scales behind. In all the other species it touches three or four. 



Marginals. — I apply this term to certain small cuneate scales which are, in many 

 species, intercalated between the infralabials at the labial margin. They are very 

 distinctive in form, and not to be confused with divided infralabials, the outer parts of 

 which are not cuneate in outline. Examples of divided infralabials are shown in 

 figs. 12B where the third is divided on the left side, in 24C where the first is 

 so distinguished on the left side, and in 59C where the fourth is divided on both sides. 



Their constancy though apparently complete in many species is less so in others, 

 thereby detracting somewhat from their value ; still they are fully as important as 

 many other characters upon which one has to rely in separating species, especially 

 those of the genus Distira. They are absent in D. gracilis, Z). cantoris and D. jerdoni, 

 there being no exceptions in the large series of each that I have examined. Similarly, 

 one or more are present in the large series of viper ina (20), ccerulescens (29), fasciata 

 (34), torquata (29), without any exception. In most of the other species of Distira 

 the constancy is not so complete though very striking. The constancy in the number 

 of these little shields when present is not so striking, for though a very large number 

 of individuals in many species have but one, and that wedged between the third and 

 fourth infralabials, there is a tendency for more to be present and they may succeed 

 the second infralabial. In fasciata, for instance, five specimens out of 38 have two 

 marginals occurring after the second or third infralabials on one or both sides, in all the 

 rest there is but one, and that after the third. The constancy in number and disposi- 

 tion though not complete is as striking in obscura, ccerulescens , etc. 



Sublinguals.— The "Chin shields" of other authors. There are usually two 

 pairs, the fellows of each in contact with one another. In Astrotia both pairs are 

 absent. In Hydras, Enhydris and Enhydrina they are poorly developed, especially 

 the posterior, if they can be said to be present at all ; and the anterior pair frequently 

 present though small, has the fellows widely separated. In Distira major, D. ornata 

 and D. ccerulescens they may also be small, but the anterior pair is very generally 

 present and the fellows in contact; the posterior, when recognisable, are usually well 

 separated by small scales. 



The contact or separation of the posterior pair when developed, though showing 

 great constancy in some species, manifests frequent variation in individuals of other 



