102 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 



MoDODONTA ARATA, Lyc. Tab. XLV, fig. 19. 



Testa trocJdformi, spira elevata, anfractibus (6) latis, concavis, postice et antice carina, 

 striata, obtusa, suturis valde impressis, anfractibus semel concentrice tenuissime lineatis et 

 decussatim oblique striatis; basi lineis concentricis majoribus et minoribus alternatis ; 

 sulco columellari magno et dente obtuso. 



Shell trocliiform ; spire elevated ; volutions (6) wide, concave, having a striated obtuse 

 keel upon their posterior and anterior borders; there are also very delicate encircling 

 lines, which are indented by oblique decussating striations ; the base is concentrically 

 lineated, the lines being alternately large and small ; there is also a conspicuous colu- 

 mellar groove and obtuse tooth ; the apertui-e is nearly circular. 



Height and basal diameter nearly equal. 



Geological Position and Locality, The Forest Marble of Laycock ; in the collection 

 of W. Walton, Esq. 



MONODONTA TEGULATA, Lyc. Tab. XLV, figs, 17, 18. 



Testa sub-trochiformi, spira elata, anfractibus (4), latis, in medio angulatis, carinis, 

 tribus cingendis, swperne oblique planatis, in/erne concavis, anfractibus semel concentrice 

 lineatis, lineis granosis, striis tenuissimis decussatis ; basi concentrice lineatis, sulco magno 

 nmbilicali et sulco et dente obtuso instructo. 



Shell sub-trochiform ; spire elevated, consisting of four wide and carinated volutions, 

 angulated in their middle portions by a prominent encircling keel, a keel being also 

 placed at the anterior and posterior border of each volution; between the carinas are 

 numerous regular encircling lines, rendered granulated by decussating very fine obhque 

 striations ; the base is concentrically lineated, and has a large umbihcal groove bounded 

 by a prominent keel ; the columeUar sulcus and tooth are also conspicuous ; the aperture 

 is subcircular, its outer border impressed by the carinee. 



The diameter at the base is one third greater than the height. A pretty species, with 

 strongly sculptured ornamentation. The volutions are obliquely flattened above and con- 

 cave beneath the median carina. 



Geological Position and Locality. The Forest Marble of Laycock ; in the collection 

 of W. Walton, Esq. 



