48 Mr. Broderip and Mr. G. B. Sowerby on Mollusca. 
the centre, and bearing a striking general resemblance to the external 
plates of a Land-tortoise’s shell. The orifices are very small, and are 
surrounded by six triangular valvules, each transversely striated, and 
when shut, rising from the surrounding surface in the form of a cone. 
The lower or cup-like part is formed of a coriaceous substance, with 
slight traces of separation into plates, but without internal muscular 
fibre. In one specimen only there were two irregular somewhat horny 
plates at the external base of the cup, but not so strongly marked as the 
upper plates. These lower plates were not to be observed in another 
specimen which was removed for the purpose of examination from the 
stone to which it was fixed. 
The learned and accurate anatomical observations on the natural 
group of Tunicata, by William Sharpe MacLeay, Esq., (Linn. Trans. 
Vol. XIV. p. 527.) have done so much in elucidation of the hitherto 
obscure structure of many of these animals, that the specific name above 
recorded is but a small tribute to the author of such a valuable 
memoir. 
DENTALIUM FILOSUM. 
D. testd gracili, tenuz, albd, filis octo longitudinalibus, striis transversis 
ereberrimis ; long. 2,5; poll. lat. =%; poll. 
Hab. ad littora maris ad Tennasserim. 
Distinguished from D. octogonwm, by its much more slender shape, 
and its thinner shell ; instead of the eight angles of that species, it has 
eight distinct, raised, longitudinal threads, Three specimens of this fine 
species were lately brought to England by Mr. Hay, who himself picked 
them up on the coast of Tennasserim. 
CyYTHEREA PLANULATA. 
C. testa trigond, depressiusculd, subequilaterali ; angulis inferioribus 
rotundatis ; pallidée flavicante, radiis numerosis fuscescentibus ; 
intus albidd, fusco-violaceo varid ; dente postico remoto ; long. 15°F 
poll. lat. 7; poll. alt. 1,5 poll. 
Hab. in littoribus Oceani Pacifici, prope Mazatlan. 
A pretty species of Cytherea, which has so much of the general ap- 
