290 Messrs. Alder and Hancock on two new species of the following extract from the translation of his paper on the Cystidea* will prove: — "Mr.. Austin states that Sycocrinites exhibits three dorso-central plates," &c (see Annals of Nat. Hist vol. xi. p. 206). "This is manifestly the description of a Crypt ocrinite (so named in 1840) ; but this author does not state the locality of his specimen," &c. I will only add, that Cryptocrinus is a genus arranged with Von Buch's family of Cystidea, and that it does not appear to belong to a group along with Pentremites* August 9th, 1851. XXIII. — Descriptions of two new species of Nudihranchiate Mol-lusca, one of them forming the type of a new Genus. By Joshua Alder and Albany Hancock. With the Anatomy of t/ie Genus, by Albany Hancock. [With two Plates.] The Nudibranchiate Mollusks, which we have now the pleasure of introducing for the first time to the notice of naturalists, we owe to the persevering researches of our friend Mr. W. P. Cocks of Falmouth, by whom they have been communicated to us, with kind permission to publish descriptions of them. The first spe-cies we shall notice we refer to the Thecacera of Fleming, a genus at present so imperfectly understood that any addition to our knowledge of its characters may be considered as furnishing a desideratum in this family of the Mollusca. We propose to characterize it as follows : — Thecacera virescens. Body rather convex, smooth, of a light peach-blossom tint, blotched with green anteriorly and poste-riorly. Head with a plain sub velar margin in front. Ten-tacles broadly laminated, the laminated portion green, the lower or smooth portion of the same colour as the body ; they are retractile within moderately-sized sheaths with smooth margins. Branchial plumes five, green, margined with white. A single row of obsolete tubercles encircles the branchial re-gion. Foot of a dull yellowish white. Length T 3 n ths of an inch. This beautiful little animal differs in several respects from the Doris pennigera of Montagu, which is the type of the genus The-cacera, and might by some naturalists be thought entitled to rank as a new genus ; we prefer, however, to consider it an ab-* A translation of this paper appeared in the Journal of the Geological Society, Feb. 1st, 1846.
XXIII.—Descriptions of two new species of Nudibranchiate Mollusca, one of them forming the type of a new genus. With the anatomy of the genus, by Albany Hancock
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