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Show 42 PROF. F. J. BELL ON ECHINANTHUS TUMIDUS. [Jan. 15, disposition of these odd pores to call to mind the characters of an Echinolampas. The madreporite occupies the centre of the apical area, and the five genital pores are quite distinct; the two smallest are those that lie to the left, and the anterior one on the right is a little smaller than the other two; between these last lies an ocular pore almost as large as they; all the other ocular pores are quite small. The sutures between the coronal plates are, on the abactinal surface, remarkably distinct; the tubercles are all of moderate size, subequal, and minutely perforated at their tip ; they are not closely packed, and the intervals between them are occupied by miliaries rather coarser than those of E. testudinarius. The tubercles on the actinal surface are a little larger and rather more closely packed ; they are more deeply sunken, and the miliaries are rather coarse. Mouth deeply sunken. Owing to its injured condition it is impossible to say how much or h ow little has been removed, and I cannot follow M r . Tenison-Woods in giving an exact statement as to its size or shape. The pillars within seem, so far as one can judge by the touch, to be well developed, and are to be felt just within the margin of the injured mouth ; so that they extend over at least three fourths of the radius of the internal cavity. During life the test would seem to have been covered with primary and secondary spines, both of which were short, and the former about twice as stout as the latter; they were coarsely striated, had a strongish ring, and were probably of a yellowish-green colour, The dried test is brown, but the colour is not uniform, being darker at the ambitus than in the enclosed region; the colour below more uniformly brownish. Length 140, breadth 116, longest axis of anus 8 m m . Hab. . Mr. Tenison-Woods states that he has " every reason to think (it) came from the coast of N . S. Wales, though there is no precise information as to its habitat." The injuries received by the specimen indicate that it was speared by the pronged instruments with which flat fish are fished for in Port Jackson and its neighbourhood. Theoretical Considerations.-It will be clear enough that the generic definition of Echinanthus will have to be very considerably altered, if we allow the species now described to remain within its limits. Hardly any character is of greater importance among the Echi-noidea in general than that of the disposition of the pores in the ambulacral plates ; among the Petalosticha this character rises to be one of supreme importance, and is, I believe, the best criterion of the extent and intimacy of generic relations. In forms already known to us we find that the pores m a y be set in straight parallel rows which, at the region of the ambitus, become more or less irregular and scattered, e. g. Pala?olampas crassa ; or the pores of one half m a y be less numerous than those of the other, e. g. |