About the same time an American newspaper contained an account given by Captain O. A. Pitfield, of the steamship _Mexico_, who stated that he had ‘passed through a tangled mass of snakes’ off the Tortuga islands, at the entrance to the Gulf of Mexico. The ship was ‘more than an hour’ in passing them. ‘They were of all sizes, from the ordinary green water snake of two feet long, to monsters, genuine “sea serpents,” of fourteen to fifteen feet in length.’ I replied to both these communications at the time (_Land and Water_, April 5, 1879), inviting further information, and describing the features by which true water and true sea snakes could be easily distinguished. Nothing further appeared on the subject, and I have little doubt but that, in both cases, the ‘shoals of sea snakes’ were land species that had been merely carried out to sea by force of rivers. I have since been more strongly inclined to this opinion on learning from Dr. Stradling that similar transportations of snakes occur through the force of some of the South American rivers. ‘Do you know the snakes which belong to the River Plate proper?’ he asks me by letter. ‘So many are brought down by floods from Paraguay—even the big constrictors—that it is difficult to determine from occasional specimens.’ I could not, unfortunately, refer to any books that afforded much information on this subject; for amongst the greatest literary needs experienced by an ophiologist is some complete and special work on the South American snakes, corresponding with Günther’s _Reptiles of British India_, and Krefft’s _Snakes of Australia_. Other writers have mentioned the occurrence of boa constrictors and anacondas far out at sea occasionally, beguiling the unsophisticated into reporting a veritable ‘sea serpent’ to the _Times_ by the first homeward-bound mail. [Illustration] CHAPTER XIV. _THE PELAGIC OR SEA SNAKES._ THE modifications of ordinary forms which are seen in the fresh-water snakes are still more beautifully developed in the _Hydrophidæ_, or true marine serpents. The former, being never out of easy reach of shore, could easily find a safe harbour from violent torrents, in holes in the banks or among the strong aquatic weeds along the borders of lakes and rivers; and to be enabled to hold on to these in times of danger or of repose, they possess a prehensile power of tail. In a rough and stormy ocean, a much more powerful propeller and rudder would be necessary for the guidance of the reptile, and to afford resistance against the denser medium of sea water; therefore the tail of sea snakes is not only prehensile but strongly compressed, so as to almost form a vertical fin, answering altogether to that of a fish. This is their most conspicuous and striking feature, and one that would leave no doubt in the mind of the observer between the true marine and those fresh-water species which may by accident drift out to sea by force of current.