Mr. W. Clark on the Muricidse. 127 



port ; it rests solely on the emargination in the upper part of the 

 outer lip and the corresponding sinus of the mantle, which in 

 the British species is not cloven as in the true exotic Pleuroto- 

 mata. These slight characters, whether of the shell or the animal, 

 so far from being essential permanent ones, are most variable and 

 uncertain, shadowing in the numerous species, from the deep 

 pleurotomic scission into the simple, scarcely perceptible canal of 

 the Murices of our second section, the Fusi of authors. No one 

 can define the boundary of this arbitrary generic index, which 

 does not in many species even indicate specific variation. 



M. Philippi states that the great differences in the pleuro- 

 tomic sinuses and other organs of the minor Murices of the 

 Mediterranean, many of which are amongst our indigena, from 

 the generic characters of the trne Pleuroto7nata, induced M. Mil- 

 let to found the genus Defrancia as a depository for these aber- 

 rant species. Dr. Leach placed them in his genus Mangilia, but 

 I can see nothing in those I have described to justify the crea- 

 tion of a genus for their animals distinct from Murex. I new 

 them as Murices in which the opercnla have vanished or become 

 obsolete ; I have therefore on that account placed them as the 

 last section of the genus Murex, considering them as on the con- 

 fines of the family, and forming the passage to the exotic genera 

 Cancellaria, Dolium, Harpa, Mitra, Valuta and Conus, all of 

 which except Conus, that has a minute operculum, are without 

 that appendage ; and though these families are not the typical 

 Canalifera, still it is clear that the Columellariadte and Convolu- 

 tidce have very many points of connection with the Muricida. In 

 this section there are two or three British species, the animals of 

 which have not occurred to us ; amongst them, the Pleurotoma 

 teres, nonnull., which is placed here provisionally, being the only 

 British species without longitudinal ribs ; the animal may be the 

 true exotic Pleurotoma with an operculum ; the character of the 

 scission is peculiar, and more in accordance with that genus ; its 

 position must remain in doubt until the soft parts have been 

 examined. 



I have to say a few words on the gland which is seen in many 

 species of the Muricidce, and is conspicuous in the Murex lapillus, 

 Purpura of authors, and which has been considered by naturalists 

 to be the organ that produced the ancient far-famed Tyrian pur- 

 ple dye. The gland is of a white or green colour ; it lies between 

 the mucous fillets and the ovarium on the right side of the ani- 

 mal ; it is of linear form, and though in some species it appears 

 of a dark green colour, the juice or secretion, when extracted and 

 exposed to the air and sun, assumes the purple hue. It is 

 doubtful from what species this famous dye was obtained ; it can 



