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PLEUKOTOMARIA, Defrance. 



Gen. Char. A trocliiform spiral shell, with an 

 angular sinus near the middle of the outer lip, 

 from which a band marked with lines of growth 

 that indicate the sinus is carried round the 

 whorls ; no beak or sinus at the base of the 

 aperture ; a columella with or without an um- 

 bilicus. 



A GENUS of shells only known in the fossil state ; the spe- 

 cies vary much in the elevation of the spire, but are gene- 

 rally short shells. It is named Pleurotomaria^ because it 

 bears the same relation to Trochus as Pleurotoma does to 

 Fusus; some of the most elongated species occur in the 

 Silurian system of rocks, others are met with in various 

 parts of the series up to the greensand, where the newest is 

 found ; they are most abundant in the mountain limestone, 

 and not unfrequent in the lower oolite. The following is 

 a list of the species already published under various names 

 in the ' Mineral Conchology ' : Helix carinatus, tab. 10. f. 2 ; 

 H. striatus, t. 171. f. 1 ; H. cirriformis, t. 1 71. f. 2 ; Trochus 

 angJicus^ t. 142; T. punctatus^ t. 193. f . 1 ; T. elongatus^ 

 t. 193. f. 2-4; T.abbreviatus, t. 193. f. 5; T.fasciatus,t. 220. 

 f. 1 ; T.granulatus^ t. 220. f. 2 ; T. sulcatus, t. 220. f. 3 ; T. 

 ornatus, t. 221 . f. 1 ; T. bicarinatus^ t. 221 . f 2 ; T. reticula- 

 tus, t. 272. f. 2; T. Gtbsii, t. 278. 



