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Show 1873.] MR. R. B.WATSON ON MADEIRAN MOLLUSKS. 379 into the form and arrangement of the longitudinal bars, which, regardless of the line of the oblique ribs, score the whorls straight across. RISSOA SIMILIS, Scacchi. (Plate XXXV. figs. 16 & 16 a.) Not in M'Andrew's list. Hab. Selvagens, shore; Porto Santo, shore to 50 fathoms; Machico, 10-15 fathoms; Santa Cruz, 10-15 fathoms; Piedade (Canigal), 10-15 fathoms ; Ponta de S. Lourengo, 25 fathoms; Porto da Cruz, 50 fathoms ; Funchal, 50 fathoms. This is a most troublesome species, and would afford any species-monger ample exercise. But on a large collection of specimens it is impossible to establish even well-marked varieties, so variable and interchangeable are the peculiarities of form, sculpture, and colour. On the whole, however, there are two distinct varieties-one ribbed, the other smooth (var. levis), the former being relatively longer and broader than the other. These varieties are found quite promiscuously intermingled, only that I found the clearest, brightest, and on the whole most aberrant specimens of the var. levis among drift seaweed on the clean sandy shore of Porto Santo. Mr. Gwyn Jeffreys (Brit. Conch, vol. iv. p. 37) regards this species as a small variety of R. costulata, to which I would gladly have united it here if I could have convinced myself that that or the others of that unsatisfactory group had any better right than this species of Scacchi to separate recognition. In their present hopeless state I prefer to leave them alone. RISSOA ALBUGO, Watson. (Plate XXXV. fig. 17.) Shell conic-oblong, peculiar as being slightly spindle-shaped, from the last half whorl being contracted in its breadth and drawn out in length, glassily transparent, thin, smooth, and glossy. Sculpture. One distinct but very fine and shallow spiral furrow, like a scratch, shows itself just below the periphery but above corner of lip, and runs round to very edge of lip in front; below this tbe whole base is covered with a series of very faint equally distanced spiral lines about yAoo ^nc^ apart,very rarely visible ; above periphery a series of still fainter and more minute spiral lines can sometimes be seen, as it were, in the substance of the shell: the whole surface is covered with very faint, flexuous, longitudinal lines of growth; these alone are traceable on upper whorls. Colour, when fresh, transparent glassy white, with a yellowish tinge, dotted with minute, yjjQ-inch square, crimson, angular dots, arranged in series of spirals 10 to 20 in number, about as numerous above the spiral furrow as below it; these are sometimes arranged at such regular intervals in the successive spirals as to form perfect squares; in other specimens they become, above the periphery, longitudinally confluent in pairs so as to form couples of little longitudinal crimson lines (about twelve couples on last whorl, fewer on preceding), somewhat irregular, interrupted, and flexuous; each pair are parted from the next set by a space somewhat broader than |