MAZATLAN UNIVALVES 235 



293. OMPHALIUS LIGULATUS, Mke. 



! 



Trochus ligulatus, Zeit.f. Mai. 1850, P- 173, no. 34. 



?= Phorcus Californicus, A. Ad. in Proc. Zool. Soc, 1851, 



p. 157, no. 17 : (Omphalius C.) H. $ A. Ad. Gen. i. 429. 



[Phorcus, Risso, teste A. Ad. = Omphalius, P/iil. : teste 



Phil.= Trochus Magus &c. = Gibbula, Leach, H. fy A. Ad.~\ 

 Comp. Phorcus liratus, A. Ad. loc. cit. no. 15 : (Omphalius 1.) 



H. $ A. Ad. Gen. i. 429. 



Shell about the shape and size of Phorcus (G-ibbula) ciner- 

 arius, which takes its place in the Atlantic fauna, as P. unibili- 

 caris does that of O. viridulus. Outside crowded with more 

 or less fine, more or less subnodulose spiral ridges, of which 

 one or more are occasionally more developed than the rest. 

 Umbilicus more or less open to the top, where the thin nuclear 

 part is generally punctured. Whirls 7, of which the first three 

 are smooth and flattened. Mouth slanting : parietal callosity 

 near the umbilicus, not projecting ; columella between this 

 and the spiral ridge deeply sinuated ; spiral ridge ending in a 

 broad diagonal callosity, close to which on the labiuni is a 

 small tubercle, and at the base of the shell a large one. The 

 area between these tubercles and the layer is rather deeply 

 but shortly channeled. From the basal tubercle (in the adult 

 shell) runs a callus round the inside of the base of the labrum 

 which is sometimes subnodulous. Between this callus and 

 the outer lip is a well marked channel. Shell outside covered 

 with a rough brown epidermis, conspicuous between the ridges. 

 The shell, even when young, is generally covered with Annelids, 

 Bryozoa, &c. Colour beneath the epidermis brownish purple, 

 or ashy brown, spotted in shades. Operculum outside deeply 

 concave, (div. 150,) of about 20 whirls, not thin, thickened at 

 the margin, leaving a distinct suture, not striated; inside 

 glossy, of an orange horn colour. A specimen of ordinary 

 growth measures long. "69, lot. '77, div. 80. 



A flattened sp. '47, '93, 100. 



A conical sp. "74, "74, ,, 70. 



Hob. Mazatlan ; common ; Ifpool Col. 



Tablet 1133 contains 5 sp. whirls somewhat rounded, depres- 

 sed. 1134, 4 do. somewhat depressed. 1135, 4 do. typical 

 form. 1136, 5 do. conical. 1137, 5 sp. whirls flattened, depress- 

 ed. 1138, 3 do. ordinary form. 



Tablet 1139 contains 3 sp. ribs very fine. 1140, 3 do. nodul- 

 ous. 1141, 2 do. curiously mended after fracture. 1142, 4 do. 



