TYMPAN03TOMA. 283 



Turbines are mostly tropical. — Obs. The only certain means of 

 distinguishing this extensive genus of marine shells from Trochus, 

 is the operculum, which in the latter genus is horny, spiral, 

 and composed of a great number of whorls. The Trochi, however, 

 are in general more conical, and flatter at the under side of the 

 whorls, and this constitutes Lamarck's distinction between the 

 genera, T. setosus, fig. 368. 



TURGID. (Turgidus.) Puffed up, swollen, inflated. This term 

 is applied synonymoi-Jy with Ventricose. 



TURRICULA. Humph. Melania, Auct. 



TURRICULACEA. Bl. The seventh family of the Order Poly- 

 thalamacea, Bl. containing the genus Turrilites, fig. 483. 



TURRILITES. Lam. (Tun-is, a tower; Xidog, a stone.) Fam. 

 Turriculacea, Lam. Ammonacea, Bl. — Descr. Chambered, turrited, 

 spiral ; septa sinuous and lobate, perforated by a siphon ; aper- 

 ture rounded, with the outer lip expanded. This genus, which is 

 distinguished from the other Ammonacea by having the spire 

 produced, i. e. not being convolute, consists of several species, 

 occurring only in chalk-marl. Fig. 483. 



TURRIS. Montf. A genus composed of those species of Mitra, 

 Auct. which have the whorls angulated, with the aperture length- 

 ened and undulated. 



TURRITED. The spire of an univalve shell is said to be turrited 

 when the whorls of which it is composed are regulated so as to 

 have the appearance of little turrets rising above each other, as 

 in Mitra, fig. 431. 



TURRITELLA. Lam. (A little tower.) Fam. Turbinacea, Lam. 

 Cricostomata, Bl. — Descr. Turrited, elongated, generally grooved 

 spirally ; spire pointed, consisting of numerous whorls ; aperture 

 rounded or angulated ; inner and outer lips thin, confluent 

 anteriorly ; operculum horny. — Obs. The shells composing this 

 well defined genus, are commonly called screws, a name to which 

 the spiral grooves of most of the species seems to entitle them. 

 Fig. 3/0, T. imbricata. 



TYMPANOSTOMA. Sebum. (Timbrel mouth.) Potamis, Brongn. 



