BRITISH FOSSILS. 



Desor's figures and descriptions, that the species in question is distinct 

 from D. hicordatiis ; and certainly, industriously as the Survey collectors 

 have ransacked the inferior oolites of Dorsetshire, I have never received 

 any other species of Dysaster from thence, except Dysaster ringens^ as 

 here described, and Dysaster bicordatus, a very different form, of which 

 Mr. M 'Coy's D. symmetricus is an oval variety. 



The following table of the dimensions of eight specimens, in inches 

 and twelfths, from the Bridport oolite, will show the variable propor- 

 tions of this species. 







A. 



B. 



c. 



D. 



E. 



F. 



G. 



H. 







Length . 

 Breadth . . 

 Thickness . 



1 



Oil. 



0\\ 



Of. 

 OA 



o?i 



Oil 

 OA 



OtI 

 OtI 



OA 



oii 



OA 



oifi 

 o?| 

 OA 





Localities and Geological Position. — This species has been collected 

 abundantly by Mr. Bristow and Mr. Gapper during the examination in 

 the course of the Geological Survey of the Inferior oolite of Somer- 

 setshire and Dorsetshire. It appears to occur chiefly in the sands of 

 that formation, and is very generally the companion of Galerites {Ilolec- 

 typus) hemisphcBrica. Among the localities from whence I have 

 examined specimens are the following : Lyttelton-liill, near South Cad- 

 bury ; between Sherborne and Yeovil ; Little Windsor ; Stoke Knaps. 

 Greenland (in the ferruginous beds), Loders ; Whatley ; Smokeham ; 

 Honeycombe ; Bradford Abbas ; Beaminster ; Shipton Gorge, where it is 

 accompanied by Dysaster hicordatiis ; Burton Bradstock ; Burton Cliffs 

 (top beds) ; near Bridport Harbour ; Chideock-hill ; Mapperton ; West 

 Swillets. The places mentioned are included in sheets 18 and 19 of 

 the Ordnance Survey Map of England. 



Foreign Distribution. — In the Marnes Vesuliennes'' of the Jura 

 (Agassiz) ; in the ferruginous oolite of Normandy (Deslon champs) ; in 

 the ferruginous oolite of the Tour-du-Pre (Cotteau). 



Explanation of the Plate. 



Fig. 1. View of body seen from above. 



Fig. 2. Underside of same specimen. 



Fig 3. Terminal view. 



Fig. 4. Terminal view of a wider specimen. 



Figs. 5 and 6. Profile of variations in proportions of specimens. 



Fig. 7. Diagram of structure of test, the plates of the disk and those above the anus not 

 made out. 



8. Oral terminations of the ambulacra, showing the triplication of the pores. 



9. Kelative proportions of ambulacral and interambulacral plates, taken from the sides. 



10. Tubercles and granules of surface. 



11. Genital disk, terminations of anterior ambulacra, and madreporiform plate. 



June, 1850. Edward Forbes. 



