GASTEROPODA PECTINIBRANCHIATA. 367 



able, however, for a bed formed of calcareous matter, on which it 

 rests, and which probably exuded from the foot of the animal(l). 



Crepidula, Lam. 



The shell oval, with an obtuse horizontal point, directed obliquely 

 backwards and laterally; the aperture forming the base of the shell, 

 which is half closed beneath and behind by a horizontal plate. The 

 abdominal sac which contains the viscera is on this plate, the foot 

 beneath, and the head and branchise forwards. The latter consist 

 of a range of long filaments attached under the anterior margin of 

 the branchial cavity. The eyes are at the external base of two coni- 

 cal tentacula(2). The genus 



PiLEOLUs, Sowerby, 



Appears to consist of Crepidulae, in which the transverse plate oc- 

 cupies half the aperture; their shell, however, is more like that of 

 a Patella(3). They are only found fossil. 



Septaria, Fer. — Navicella, Lam. — Cimber, Montf., 82. 



The shell resembles a Crepidula, except that the summit is symme- 

 trical and laid on the posterior margin, and that the horizontal plate 

 is less salient. The animal is also provided with an additional, 

 irregularly shaped, testaceous plate, horizontally connected with the 

 superior surface of the muscular disk of its foot, and covered by the 

 abdominal sac, which it partially supports. It is probably analo- 

 gous to an operculum, but does not exercise its functions, being, in 

 a measure, situated internally. The animal has long tentacula, at 

 whose external base are pedicles which support the eyes. They in- 

 habit the rivers of hot countries(4). In the 



(1) Patella cornucopias. Lam., Knorr., Petrif., II, part ii, pi. 131, f. 3, andBlainv,, 



Malac- 

 ca) Patella fmmicata, hist. 545, 33,35; — P. aculeata, Chemn., X, clxviii, 1624 — 



25; — P. Goreensis, Martini, I, xiii, 131, 132; — P.solea, Naturf., XVIII, ii, 15; — P. 



crepidula, Adans. Seneg-., I, ii, 9; — P. poreellana, List., 545, 34. 



S (3) Pileolus plicatus, Sowerb.; — Pil. l3evis,Id., Genera of Shells, No. IX; — Pil. 



neritoides, Desh., Ann. des Sc. Nat., I, xiii, 3, a, b, c. 



(4) Patella nerito'idea. List., 545 — 36, and Naturf., XIII, v, 1, 2; — Pat. borbon- 



ica, Bory Saint-Vincent, Voy. I, xxxvii, 2; and for the animal, Quoy and Gaym., 



Voy. de Freycia., pi. 71, f. 3 — 6. 



