OCR Text |
Show 1891.] OF PLEUROTOMARIA FROM TOBAGO. 485 The next discovery of Pleurotomaria was in 1861, when a single imperfect specimen of another species came to light. This was described as PL adansoniana in the ' Journal de Conchyliologie' for that year (p. 163, pi. v.). This example was 80 millimetres in width and 74 in height. Another more perfect specimen of this species was taken near Guadelupe, and described in Journ. de Conch. 1882, p. 12, pi. i. This one was 85 millimetres in height and 91 in diameter. It is to this species that the Tobago shell is to be referred. Besides the two examples named above, three others are known. Two other living species of Pleurotomaria have been described- namely, PL beyrichi in 1877 and PL rumphii in 1879. The former was found in Japanese waters, and of it four examples are known. The latter is stated to be from the Moluccas, and only a single specimen is known. Consequently, according to the enumeration given in Woodward's paper, there were up to the present time thirteen specimens of recent Pleurotomaria in existence, belonging to four species. The Tobago specimen is therefore the sixth of the species and the fourteenth of the genus known as recent. The dimensions of PL quoyana and PL adansoniana have already been given: those of the other two species are indicated below :- Height. Diameter. PI. rumphii 170 mm. 190 mm. PL beyrichi 82 „ 83 „ The dimensions of the present specimen of PL adansoniana are as follows :-Total height 150 m m . ; greatest diameter 160 mm.; height of aperture 50 m m . ; width of umbilicus 30 m m . ; length of fissure 220 mm.; width of fissure 5 m m . This, therefore, is the second in size of the specimens of recent Pleurotomaria in existence, being, in fact, very nearly as large as the unique specimen of PL rumphii, and leaving all the other known examples of the genus a long way behind. The coloration consists of a number of flames or irregular more or less zigzag spots of flesh-red passing into orange, arranged on a ground of very pale flesh tint. The apex is finely pointed, yellow, and almost smooth. When viewed through the funnel-shaped umbilicus and held to the light, it appears almost transparent. The supra-median fissure occupies the larger half of the contour of the shell. The characters generally correspond very closely with those given in the ' Journal de Conchyliologie,' 1882, p. 12. The colour of our specimen would appear, if we may judge by the figures, to be paler than the previous examples. It is in almost perfect condition, and looks as if when found it had had the soft parts in place. It is merely slightlv house-worn, as an article which had been kept as a drawing-room ornament for several years would be. As has been noticed, the habitat of Pleurotomaria is in deep water on rocky bottoms. Consequently it is probable that recent shells of this genus will always be rare ; for not only is it difficult to procure shells living in such conditions, but the conditions themselves are of very restricted occurrence. |