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Show 1883.] ' L I G H T N I N G ' A N D ' PORCUPINE'EXPEDITIONS. Ill in a small but deep perforation and is enclosed by a more or less and distinct ridge. The tentacles of the animal are ciliated as in Trochus and Rissoa, which is not tbe case in Lacuna. The shell varies in tbe comparative height of the spire, as well as in the sculpture as shown in the variety costulata. That variety is Lacuna margaritifera of Watson. 2. CITHNA CINCTA \ Jeffreys. (Plate XX. fig. 8.) S H E L L globosely conical, thin, opaque, rather glossy : sculpture, a few and remote spiral striae, of which there are from 3 to 6 on the last whorl and 1 or 2 on the penultimate and other whorls ; the most prominent of these striae is one below the suture, which gives tbe whorls a somewhat carinated appearance; this stria is minutely tubercled on the upper whorls : colour white : spire turreted, ending in a twisted point : whorls 5, swollen ; the last exceeds two fifths of the whole shell, the others gradually enlarging : suture deep : mouth circular, bluntly angulated at the base : outer lip thin, slightly expanding, and folded over the pillar : inner lip attached to the pillar: umbilicus shallow, enclosed by a semicircular ridge and ending in a small but deep perforation. L. 0*1, B. 0*1. ' Porcupine ' Exp. 1870 : Atl. St. 16. Two specimens. 3. CITHNA CARINATA2, Jeffreys. (Plate XX. fig. 9.) S H E L L compactly pyramidal, thin, opaque, glossy : sculpture consisting of a single keel which surrounds the periphery or middle of each whorl and makes it angular; under the microscope the surface appears closely granular or fretted; the base is encircled by a few slight striae : colour white, except as to the uppermost whorls, which are as in C. tenella yellowish-brown : spire turreted, ending in a symmetrical apex : whorls 5-6, angulated, flattened between the suture and the keel, regularly increasing in size : suture very deep : mouth quadrangular, sharply pointed at the base : outer lip thin, reflected behind : inner lip narrow, attached to the pillar: umbilicus saucer-shaped, enclosed by a slight and inconspicuous ridge and terminating in a small perforation. L. 0*1, B. 0*1. ' Porcupine ' Exp. 1870 : Atl. St. 16. A single specimen. 4. CITHNA ADAMSI3, Jeffreys. (Plate XX. fig. 10.) S H E L L having the shape of a Helix, nearly globular, thin, semi-transparent, and glossy : sculpture none except the umbilical ridge : colour white : spire rather short: whorls 4|, convex, the last occupying more than two thirds of the shell, and the others being in the same relative proportion ; apex slightly twisted : suture very deep : mouth circular, bluntly pointed at the base : outer lip thin, folded partly over the umbilicus : inner lip adhering io the pillar : umbilicus small and narrow, enclosed by a sharp and nearly semicircular ridge ; perforation scarcely perceptible. L. 0*0625, B. 0*075. 1 Encircled. . 2 Keeled. 3 Named in honour of the memory of the late eminent malacologist Mr. Arthur Adams. |