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Show 130 • MR. CYRIL CROSSLAND O N T H E [June 16, distinctions, the proportions of which are described numerically and with great minuteness by some of the best workers. However one may admire the care which has been employed, and however desirable the use of such numerical statements may be, m y results showed clearly that they are, from the nature of the case, unpractical. As their employment can only render descriptions more cumbrous, and the limits of the species so defined more hazy even than in nature, I forego all minuteness in statements of proportion and numbers. Accurate figures, drawn to scale, will provide as full and unmistakable accounts of species as is possible by the medium of ink and paper, the extent of variation rarely being so great as to render a drawing thus prepared from one specimen not recognisable at once as a likeness of any other-member of the same species. The deductions from m y tables of measurements of specimens of Marphysa mossambica are shortly as follows :- (1) The body shape is generally constant, but the numerical position of the widest segment may be very different in certain individuals. (2) The proportions of pro- and peristomium in se and inter se are roughly constant. (3) The length of the unpaired tentacle is variable within limits, but the number of the segment to which it reaches when laid along the back is not worth giving in a description of the species. (4) The gills, as often noted, begin on different segments in different specimens, increase in size and complexity quite irregularly, and vary in the maximum number of the filaments they bear. In another examination, all the smaller gills were left out of account, the distance from the anterior end to the point where gills of approximately the full size begin to occur being measured. This varies from 5 to 6 cms.; the number of segments it contains varies from 64 to 80. (5) The number of teeth borne by the dental plates frequently varies by one on either side of the mean, i. e. for the larger-plates from 4 to 6. In Marphysa belli, a species which is characterised by the large size and the concentration of the gills to a few segments, these still vary in the same ways. Two specimens, collected and preserved together*, differed as follows :- Though both are 3*5 m m . in breadth the segments in no. 1 are much the shorter. In no. 1 the gills do not meet over the back, though no. 2 agrees with the specific definition in this respect. No. 1 bears 17 pairs of gills on feet 13 to 30 t, and no. 2 21 pairs * I owe m y opportunity of examining this species to the kindness of Prof. Mcintosh. The specimens were dredged by the ' Porcupine' in 1870 from 81 fathoms, off Cape Finisterre. f In all cases the first setigerous segment is counted as the first, a method of reckoning which is free from any possible ambiguity. |