54 MOLLUSCA. 



* 



Several are flattened, with a trenchant edge, which has caused them 

 to be compared to the rowel of a spur Calcar, Montf.* 



Some again are slightly depressed, orbicular and shining, with a 

 semi-round aperture, the columella convex and callous Rotella, Lam.f 



The columella of others is distinguished near the base by a little 

 prominence, or vestige of a tooth, similar to that of the Monodontcs, 

 from which these Trcchi only differ in the angle of their aperture, 

 and the projection of their margin. The aperture is usually about 

 as high as it is wide Cantharis, Montf.J 



In some of them, on the contrary, the aperture is much wider than 

 it is high, and their convex base approximates them to the Calyp- 

 tracea Infundibulum, Montf. 



In others again, where the aperture is also much wider than it is 

 high, the columella forms a spiral canal ||. 



Those which have a turreted shell approach Ccrithium Telesco- 

 pium, Montf .^ 



Among the umbilicated Trochi, there are some in which there is no 

 projection in the columella; most of them are flattened, and have the 

 external angle trenchant. Of this number is 



Tr. agylutinans, L. ; Chemn., V, clxxii, 1688, 9. Remarkable 

 for the habit of glueing to its shell, and even incorporating 

 with it, as fast as it increases in size, various foreign bodies, 

 such as little pebbles, fragments of other shells, &c. ; it frequently 

 covers its umbilicus with a testaceous plate**. 



The margin of others, however, is rounded, such as 



Tr. cinerarias, L.; Chemn., V. clxxi, 1686. A small species, 

 and the most common on the coast of France; greenish, ob- 

 liquely streaked with violet. 



Some umbilicated Trochi have a prominence near the bottom of 

 the columella ff . 



And, finally, there are others in which it is longitudinally cre- 

 nateJJ. The 



* Turbo calcar, L., Chemn., V. clxiv, 1552; T. stellaris, Id., 1553 ; T. aculcatus, 

 Id., 1554 57; T. imperialis, Id., 1714. 



f Tr. vestiarius, L., Chemn., V. clxvi, 1601. 



31 J Tr. iris, Chemn., 1522 23; Tr. granatum, Ib., 1634 55; Tr. zyzyphinvs, 

 Ib., clxvi, 1592 98; Tr. comts, clxvii, 1610; Tr. mantlatus, clxviii, 1617 18; 

 Tr. americanus, clxii, 1534 35; Tr. conulus, Gualt., LXX, M. 



Trochus concavus, Chemn., V, clxxviii, 1620, 21. 



|| Trochus foveolatus, Chemn., V, clxi, 1516 19; Tr. mauritianus, Id., clxiii, 

 1547 48 ; Tr.fcnestratus, Ib., 1549 50; Tr. obeliscus, clx, 1510 12. 



Tf Trochus telescopium, Chemn., V, clx, 1507 9. 



** Add, Trochus ludicus, Chemn., V, clxxii, 1697 98; Tr. ImperiuUs, clxxiii, 

 1714, and clxxiv, 1715; Tr. solans, Ib., 17011702, and 1716 1717 ; Tr. 

 planus, Ib., 1/21, 1722. 



ft TV. virgatus, Chemn., V. clx, 1514 15; TV. nihticus, Chemn., V. clxvii, 

 1605 7, clxviii, 1614; Tr. verrnts, Id., clxix, 1625 26; 7V. inftqualis, clxx, 

 1636 37 ; Tr. magnus, clxxi, 1656 57 ; Tr. conspersus, Gualt., Ixx. B. ; Tr. 

 jujubinuSj clxvii, 1612 13. 



JJ Tr. macutatus, clxviii, 1615 1616; Tr. costatus, clxix, 1634; Tr. riridis, 

 clxx, 1644; Tr. radiatus, Ib., 1640 42. 



