OF MOLLUSCA. 203 



The lingual membrane of S. testudinaria is broad, short, with 

 very numerous close longitudinal series of slender, curved, acute, 

 subulate teeth, placed in close oblique cross rows, without any central 

 series. 



3. Oscanius. 



Mantle expanded, irregular. Foot very large, expanded. Shell 

 thin, membranaceous, silvery. 



1. O. membranaceus, t. 103. f. 12; Forbes fy Hartley, Brit. Moll. 



t. X.X. f. 2. 



2. 0. Lesueurii, t. 166. f. 2. 



3. O. dilatipes, Adams, Gen. Moll. t. 60. f. 5. 



The branchial plume of Oscanius membranaceus is composed of 

 two gently arcuated leaves, tapering from their bases to a pointed 

 extremity ; each leaf consists of about twenty-five linear vessels or 

 processes, resembling a twisted cord with a longitudinal depression 

 in its centre, which is the branchial artery, and crossed on each side 

 by transverse lines ; these cord-like fillets are closely packed toge- 

 ther and taper to their terminations, which float free. The two 

 portions of the plume fold on each other, with fine short cilia on 

 each of the striae, to beat the water and eliminate air therefrom. — 

 Clark, Moll. p. 269. 



** Mantle indistinctly edged. Shell none. 



4. Neda. 



Mantle small, indistinct. Foot broad, dilated, rounded behind ; 

 lateral appendage dilated, cut on the sides, arcuate. 

 1. N. luniceps, t. 167. f. 2 ; Adams, Gen. Moll. t. 61. f. 1. 



5. PleurobranchjEA. 



Mantle small, indistinct. Foot narrow, oblong; lateral append- 

 ages forming a narrow veil. " Eyes small, at the hinder base of the 

 hinder tentacles." — Chiaje. 



1. P. Meckeli, t. 168. f. 1, 3, t. 173. f. 2, 3 (from life), t. 220. f. 3 



(young). 



2. P. maculata, t. 22. f. 12. 



The proboscis in the living animal is always retracted, but when 

 languid, or in spirits, generally exserted, thick and truncated. The 

 lingual membrane broad, dark brown, longitudinally folded, with 

 very numerous, crowded, longitudinal series of elongate, subulate, 

 slightly curved, acute, transparent teeth, in crowded oblique cross 

 series. 



Fam. IX. TYLODINAD^! (from p. 63), add— 



Shell exterior, thin, with a thick periostraca ; apex subcentral ; 

 nucleus globular, spiral, sinistral. Muscular scar ring-like, with a 



