366 ME. W. HILL ON THE LOWEE BEDS OF THE UPPEE 



Bubcordate base (see PL XII. fig. 2) ; the posterior border is not 

 truncated, but only flattened or hollowed below the vent ; there is 

 DO dorsal carina. The under surface is always flattened, and the 

 test is so elevated that the horizon of greatest width is always nearer 

 the base than the apex, and the sectional outline often resembles 

 that of EcJiinoconus suhrotimdus. The vent is always below the 

 horizon of greatest width, and its height above the base is generally 

 one fourth of the elevation of the test. The anteal sulcus is hardly 

 visible from the top. It may also be noticed that typical specimens 

 of Holaster subglohosus are abundant in Lincolnshire and Yorkshire, 

 but that specimens of large size are rare, while a small and pre- 

 sumably young specimen of H. rotundus from Speeton presents the 

 same characters as the adult individuals from Louth (PL XII.). 



Prom the larger varieties of H. Icevis this species can easily be 

 distinguished by its circular outline, its size, height, and great 

 tumidity, as well as by the feebler development of the anteal 

 sulcus. 



Locality and Position. — Lincolnshire and Yorkshire ; ranging from 

 the base of the Chalk Marl just above the Eed Chalk to the highest 

 part of the Lower Chalk. It is not at all uncommon in the chalk 

 with pink bands of Louth, and occurs also in equivalent beds at 

 many other localities in Lincolnshire ; llr. Hill has obtained it from 

 Speeton and Ganton in Yorkshire, and I saw a specimen of this 

 species in Mr. Mortimer's Museum at Driffield in 1880. 



EXPLANATION OP PLATE XII. 



Figs. 1 & 2. Pull-grown specimen of Holaster rotundus, from Louth : (1) pos- 

 terior aspect, (2) upper surface, outline slightly subcordate. 

 3. Under surface of a nearly circular specimen, from Louth. 

 4 ife 5. Posterior and anterior views of a small specimen from the Lower 

 Chalk of Speeton Cliff. 

 6. Under surface of the same specimen, showing the continuous 

 poriferous zones, which are made conspicuous by the infiltration 

 of oxide of iron. 



All the figures are of the natural size, and the originals are in the Museum 

 of Practical Geology, Jermyn Street. 



DiscTJssioir. 



The Peesident commented on the singular fact that English 

 geologists, who were among the first to recognize the main divisions 

 of the Cretaceous system, should have been the last to define the 

 zones in the Chalk. Mr. HiU, with others, had contributed to 

 remove this defect. 



Mr. Etheeidge observed that the detailed correlation of the beds 

 of the south with those of Lincolnshire and Yorkshire had never 

 been attempted before. He felt sure that in investigating the 

 relations of the Hunstanton Limestone at Speeton we could not go 

 wrong in i)lacing it with the Gault. He referred to the work of 

 Phillips, Wiltshire, and Barrois. He also spoke of the value of the 



