PLATE X. 



Soiuerbyi-zone (Concavum-beds) . 

 Figs. ] , 2.— Lioceras concavum, var. poemosum, 8. Buchman. 



Fig. 1. — Side view of a very fine adult specimen, with extremely well-preserved 

 test and beautifully complete mouth-border. (The ribs are shown somewhat too 

 conspicuous.) Bradford Abbas, Dorset. Collected and lent for figuring by the 

 late Mr. E. Witchell, F.G.S. ; and kindly presented to me by Mrs. Witchell. 



Fig. 2. — Front view of the same specimen, showing acute ventral area and 

 compression of the inner area. 



Figs. 3, 4. — Lioceras concavum (Soioerby) variety. 



Fig. 3. — Side view of a specimen with small hollow umbilicus, showing the 

 mouth-border. The test on the specimen is well preserved, especially on the 

 ventral area. Bradford Abbas, Dorset. My collection. 



Fig. 4. — Back view of the same specimen showing ventral area and carina. 



Figs. 5 — 8. — Lioceras concavum, var. v-sceiptum, 8. Buchman, 



Fig. 5. — The thick form of this variety. Side view, showing the change from 

 V-shaped to sigmoidal ribs. Probably from Bradford Abbas, Dorset. Collected 

 by my father. 



Fig. 6. — Front view of the same specimen, showing its thicker proportions and 

 practically absent carina. Where the whorls enter the aperture the carina is 

 shown too acute. 



Fig. 7. — A young form of the specimen figured Plate IX, fig. 1. Side view, 

 showing V-shaped ribs. To compare with fig. 10. Bradford Abbas, Dorset. My 

 collection. 



Fig. 8. — Front view of the same specimen. 



Fig. 9. — Lioceeas concavum (Sowerby) variety. 

 Fig. 9. — A portion of the side view of a peculiar form, intermediate between 

 this and Lioceras v-scriptum, showing strongly -marked ribs on the middle of the 

 lateral area. Bradford Abbas, Dorset. Collected by my father. 



Figs. 10, 11. — Lioceeas apeetum, 8. Buchman. 



Fig. 10. — Side view of the type specimen, showing the open umbilicus. Brad- 

 ford Abbas, Dorset. Collected and lent for figuring by the late Mr. E. Witchell 

 F.G.S. ; and kindly presented to me by Mrs. Witchell. 



Fig. 11. — Front view of the same, showing compressed parallel sides and 

 almost absent carina. 



