GASTEROPODA HETEROPODA. 353 



but no shell has ever been observed; the snout is elongated into are- 

 curved proboscis, and the eyes are not preceded by tentacula. From 

 the end of the tail is frequently observed to proceed a long articu- 

 lated fillet, which Forskahl took for a Tsenia, and whose nature is not 

 yet very clearly ascertained. 



One species, the Pterolrachea coronata, Forsk.; Peron., Ann. 

 du Mus. , XV, ii, 8, is very common in the Mediterranean, and 

 M. Lesueur describes several from the same sea, which he con- 

 siders as different Journ. Acad. Nat. Sc. Philad., Vol. I, p. 3, 

 but which require further comparison(l). 

 M. Lesueur distinguishes the Firoloid^e, where the body, instead 

 of terminating in a compressed tail, is abruptly truncated behind 

 the visceral bundle, lb. p. 37(2). 



To these two, now well known genera, I presume we must add, 

 when better understood, the 



TiMORiENNA, Quoy and Gaym. 



Voy. de Freycin., Zool. pi. Ixxxvii, f. 1, which appears to be a Fi- 

 rola divested of its foot and bundle of viscera; and the 



MONOPHORA, Id. (3), 



Voy. de Freycin., Zool. pi. Ixxxvii, f. 4, 5, which has nearly the 

 form of a Carinaria, but is without a foot, distinct bundle of viscera, 

 and shell. 



We are not so certain that we should place there the 



Phylliroe, Peron. J 



Ann. du Mus., XV, pi. ii, f. 1, where the transparent and strongly 

 compressed body has a snout before, surmounted by two long tenta- 

 cula without eyes, a truncated tail behind, and which allows its 

 heart, nervous system, stomach, and genital organs of both sexes to 

 be seen through the integuments. The genital orifices and that of 

 the anus are on the right side, and sometimes a tolerably long penis 



(1) Firola mutica,- F. gibbosa,- F. Forskalea,- F. Cuviera, which is the Ptero- 

 trachea corotiata, Forsk,; F. Frederica, copied Malacol. IJlainv., pi. xlvii, f. 4; 

 F. Feronii. Add: Pterolrachea rufa, Quoy and Gaym., Voy. de Freycin., Zool. 

 pi. 87, f. 2 and 3. 



(2) Firolo'ida Demarestia; Fir. Blainvilliana,- Fir. aculeata. Less. 



(3) We must not confound them with the Monophorae of M. Bory Saint-Vin- 

 cent, (Voy. aux Isles d'Afr.,) which are Pyrosomae. 



Vol. II. 2 U 



