GASTEROPODA PECTINIBRANCHIATA. 77 



locomotion, is deprived of a foot, properly so called ; but the part 

 which in ordinary Gasteropoda forms the tail, is here turned under 

 it, and extends to beyond the head, where its extremity becomes 

 inflated and furnished with a thin operculum; when the animal 

 withdraws into its shell, it is this mass which closes the entrance ; 

 it is sometimes seen with various appendages, and in certain species, 

 the operculum is spiny. The head of the animal is obtuse, and has 

 two moderate tentacula, on the external sides of which, at the base, 

 are the eyes. The mouth is a vertical orifice, beneath wliich is a 

 filament on each side, that has all the appearance of a tentaculum, 

 but belonging in reality to the foot. The branchise form but a single 

 range along the left side of the roof of the branchial cavity. The 

 right side is occupied by the rectum and the spermatic canal, which 

 also transmits the ova. There is no penis, the animal fecundating 

 itself. 



The species are numerous, but not very distinct. Linnaeus 

 left them among the Serpulte *. 

 The Vermilta.', also left by M. de Lamarck near the Serpulse, are 

 similar to the Vermeti f . 



Magilus, Montf., 



The Magili have a longitudinally carinated tube, which is at first 

 regularly spiral, and then extends itself in a line more or less straight; 

 although the animal is unknown, it is highly probable that it should 

 be placed near the Vermeti \. The 



SiLiQUARiA, Brvg. 



Resembles Vermetus in the head, the position of the operculum, and 

 in the tubular and irregular shell ; but there is a fissure on the whole 

 length of this shell which follows its contour, and which corresponds 

 to a similar cleft in that part of the mantle which covers the branchial 

 cavity. Along the whole side of this cleft is a branchial comb, com- 

 posed of numerous, loose and tabular-like lamellae. Linnaeus left 

 them Avith the Serpulye, and till very lately they were considered as 

 belonging to the class of the Annelides§. 



* Serpula lumbncalis, L., Adaus., Senegal, XI, 1, and several new species, 



f Serpula friquefra, Gm., Born., Mus., pi. xviii, t. 14. 



X Magilus antiquus, Montf. II, pi. 43, and Guettard, Mem., Ill, pi. l.xxi, f. 6. 



§ Serpula anguina, L.; — Serpula muricafa, Born., Mus., Sr\''III, 16. 



N.B. M. de Lamarck considered the Siliquarite and the Vermilise as neighbours 

 of the Serpula;. M. de Blainville has approximated them to the Vermeti ; M. Au- 

 douin has lately observed and described the animal, and to him do we owe what is 

 stated above. 



