Dr. J. E, Gray on the Animal of Rotella. 179 



XX.— Ort the Animal of Rotella, Lamk. By J. E. Gray, Ph.D., 

 F.R.S., V.P.Z.S. &c. 



This animal has great affinity with that of the7VocAiV&p,butdiflfers 

 so widely in some important particulars that it appears worthy of 

 a separate description, more especially as the figm*es of the ani- 

 mal of this genus given by Quoy and Gaimard (Voy. Astrolabe = 

 Gray Mollusca, t. 38. f. 7, 8, and by Kiener, Conch, t. l = Gray 

 Mollusca, 1. 107. f. 6) do not properly represent the animal : both 

 must evidently have been taken from a species of Trochus. 



The foot is truncated in front, and when contracted in spirits 

 has a deep central groove, and the side edges folded down in 

 fi'ont. The lateral fringe is distinct, with three tentacles on each 

 side; on the front of the right side near the base of the tentacles 

 it is produced into an oblong fleshy lobe, which probably partly 

 covers the base of the shell when the animal is exposed, and 

 may deposit the peculiar callosity over the axis which charac- 

 terizes the genus. The upper part of the body has a deep 

 groove on each side separating it from the rest of the body. The 

 tentacles two, subulate, with a black longitudinal central line ; 

 the right tentacle is largest and free, ^"ith an oblong compressed 

 lobe on its hinder side, which has an indistinct indication of an 

 eye on the inner part of its upper edge ; hence I am inclined to 

 consider it as a modified eye-pedicel. The left tentacle is smaller 

 and partly attached to the upper side of the left eye-pedicel, 

 which is cylindi'ical, bearing a very distinct eye, and with a large 

 membranaceous expansion attached to the whole length of its left 

 side, which is fringed with small black beards or tentacles on its 

 edge ; this expansion is folded first over the mouth towards the 

 right tentacle, and then folded back to the left side of the head 

 and continued by a slightly elevated ridge to the front edge of 

 the left lateral fringe, being a modification of the appendages 

 near the base of the tentacles found in other Trochidce. There 

 is no muzzle, as in the animal of that family, but a small circular 

 sunken hole under the base of the fringe veil emitting a short 

 cyhndi'ical retractile proboscis, armed with an elongated linear 

 lingual membrane. The teeth, as figured by Loven, are, as in the 

 Trochida, placed in many oblique ridges on each side of the lin- 

 gual membrane ; they are subulate, suddenly bent at the end, and 

 tinely denticulated near the tip ; the innermost series is com- 

 pressed and suddenly dilated from just under the bend. The 

 operculum is orbicular, horny, thin, of many gradually enlarging 

 whorls, finely cihated on the outer edge, and leather concave 

 externally. 



Since I examined the animal and made the above description. 



