182 THEONOA. 



Tilesia distorta, Bronn and Romer, 1851, Leth. Geogn. ed. 3, Bd. ii. Th. 4, 



p. 92, pi. xv. fig. 8. 

 non ,, ,, Haime, 1854, Bry. jurass. : Mem. Soc. geol. France, ser. 2, 



t. v. p. 205, pi. x. fig. 2. 

 Pictet, 1857, Traite Pal. ed. 2, t. iv. p. 130. 

 Theonoa ,, Vine, 1883, 3rd Eep. Foss. Polyz. : Rep. Brit. Assoc. 1882, 



p. 267. 

 ? ,, Vine, 1888, Polyz. Caen: Journ. Northptn. Nat. Hint. Soc. 



vol. v. p. 21. 



,, ,, Gregory, 1896, Eev. pt. vi. : Ann. Mag. Nat. Hist. ser. 6, 



vol. xvii. p. 290. 



Diagnosis. A thick encrustation. The surface is covered by 

 numerous irregular ridges, the width of which usually contains 

 two or three apertures. The depressions between the ridges are 

 deep, and usually as wide or a little wider than the ridges. 



DISTRIBUTION. 



ENGLAND : 



Inferior Oolite : near Leckhampton. 

 FOREIGN : 



Bathonian : near Caen, France. 



Description of Figure. PL X. Fig. 2. Part of zoarium, x 14 

 dia. Inferior Oolite : near Leckhampton. Brodie Coll. D. 2186. 



Affinities. Lamouroux figured two specimens as the types of 

 this species, but, as Haime pointed out, their characters are not the 

 same. Michelin, however, figured a specimen which is certainly 

 a Theonoa, and is possibly the same species as that of the second 

 of Lamouroux's figures (pi. Ixxiv. fig. 6). Haime accepted and 

 refigured Michelin's specimen as the type of Lamouroux's species ; 

 and as it is clearly a Theonoa, he merged the genus Tilesia within 

 this. 



Lamouroux's type specimens have been lost, and his figures are 

 not so satisfactory as they generally are. His figure 5 probably 

 represents a specimen of Chrysaora spinosa, Mich. ; and we may 

 take No. 6 as the type of Tilesia distorta, as Michelin and Haime 

 have done so. I doubt, however, whether their interpretation 

 of this species is correct, for their specimen has broad, continuous 

 areas occupied by apertures. There is a specimen in the Brodie 

 Collection which agrees exactly with Lamouroux's figure : this 

 I take as Theonoa distorta. It has narrow, irregular ridges. The 



