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Show 1892.] SPECIES OF EARTHWORMS. 671 always present; no ventral setce upon xviii.-Distribution : Tropical Africa, Tropical America, and India. The species Acanthodrilus novce-zelandice, A. dissimilis, A. rosce, and A. smithi (to be described in the present paper) I refer to the genus Acanthodrilus sensu stricto. I am doubtful about Acanthodrilus annectens, a species which I described some years since1. In possessing paired nephridia it agrees with Acanthodrilus (s. s.), but it has the " mucous gland " of Octochcetus, and the gonads are placed in contact with the funnels of their ducts, as is the case with three of the species which I refer to this genus, Octochcetus; it has the further peculiarity that the sperm-ducts run in the thickness of the body-wall, a peculiarity which it apparently shares with the genus Octochcetus, but which, among other Oligochaeta, is rare, and only found, so far as I am aware, in Diplocardia communis and in the not nearly allied form Siphonogaster. The absence of calciferous glands is occasionally met with in Acanthodrilus. The existence of this species serves to indicate how closely allied are the forms which do, and the forms which do not, possess a diffuse nephridial system. Another instance of the same approximation of species to each other which differ in their excretory system is afforded by Benhamia beddardi and Acanthodrilus ungulatus; in both of these there is an elaborate arrangement of modified setae and glands appended in the neighbourhood of the spermatothecae. These facts possibly indicate that the passage from the diffuse to the paired nephridia may occur more than once in a genus, and of course discount the value of the modifications of the nephridial system in classification. I shall now describe two apparently new species which I refer to my genus Octochcetus :- I. Octochsetus thomasi, n. sp.2 I have received on various occasions during the last few years examples of a small-sized Acanthodrilid from New Zealand, which I have hitherto confounded with 0. multiporus. I regarded these individuals merely as small specimens of that species. A full-sized specimen of O. multiporus is a very large worm, measuring, even in a contracted condition, some 14 inches in length by half an inch or so in breadth. On the other hand, the worms which I now consider to represent a new species of this genus are of a much more slender build. Unfortunately, I am not in a position to give any exact measurements; the specimens which I possess are none of them intact. An individual measuring 144 m m . is, I fancy, nearly complete; the diameter of this worm is not more than 5 mm., and the body consisted of 230 segments. The external characters of the species recall 0. multiporus; the prostomium is not continued by grooves on to the buccal segment. That segment and the two following are not annulate; segments 1 " On the Structure of three new Species of Earthworms &c," Q. J. M. S. vol. xxix. p. 102. „ii 2 Named after Prof. A. P. Thomas, of Auckland, New Zealand. 45* |
