THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



No. 120. NOVEMBER 1846. 



XXIX. — Notices of some new and rare British species of Naked 

 Mollusca, By Joshua Alder and Albany Hancock *. 



[With a Plate.] 



1. Description of a small Mollusk belonging to the order Infero- 



branchiata (PL IV. figs. 1, 2, 3). 

 In the month of May 1845 we found on the shores of Torbay a 

 very minute molluscous animal of a peculiar appearance, which 

 we had not before met with. It was feeding upon a small green 

 conferva in pools near high-water mark, and was only discernible 

 to the naked eye as a small black spot. On taking a piece of 

 the conferva home, and placing it in a glass of sea-water, two or 

 three of these little creatures crept out of their ambush, and were 

 found on the sides of the glass, or swimming inverted upon the 

 top of the water. On applying a lens we were immediately struck 

 with the similarity of their appearance to the animals figured by 

 M. de Quatrefages in the ' Annales des Sciences Naturelles/ under 

 the generic names of Pelta and Chalidis, and placed as the lowest 

 forms of his new order Phlebenterata. As these were the genera 

 upon which that naturalist founded his theory of extreme degra- 

 dation from the typical form in the Mollusca, we immediately 

 saw that our little animal must prove interesting in that point of 

 view, and deserving of a careful examination. A slight inspec- 

 tion of its external characters, however, was sufficient to show 

 that our captive at least did not partake of that degradation from 

 the Molluscan type which M. de Quatrefages describes in his 

 species, and that, tentacles excepted, it possessed all the external 

 organs usually found in the class Gasteropoda. The branchiae 

 formed three small plumes, placed under the posterior part of 

 the cloak a little to the right of a central tubular anus ; thus 

 bringing the species within the order Inferobranchiata of Cuvier. 

 Its characters are as follows : — 



Body limaciform, elongated, smooth, about two lines long. 



> 

 * Read at the Meeting of the British Association, Sept. 14, 184G; and 

 communicated by the authors. 



Ann. $ Mag. N. Hist. Vol. xviii. Y 



