70 ME. H. WOODS ON THE MOLLUSCA [Feb. 1 896,, 



Cenomanian than to any which occur in the divisions of the 

 Senonian and Turonian above and below it; and whereas the latter 

 are of a deep-water type, that found in the Chalk Rock is certainly 

 of a comparatively shallow-water character. 



The first mention of the Chalk Rock was made by Mr. D. Sharpe 

 in his monograph on the * Mollusca found in the Chalk of England' 

 (1855, p. d2), where he speaks of it as a ' bed of rather hard chalk,, 

 which occurs near the bottom of the Chalk with Flints, and contains 

 A. perainplus, Scaphites, and several other species of Mollusca 

 hitherto undescribed, and only known in this bed.' But the Chalk 

 Rock was first noticed under that name in the ' Catalogue of the 

 Rock-specimens in the Museum of Practical Geology ' published in 

 1860. A little later a much fuller description appeared in the 

 4 Quarterly Journal ' by Mr. Whitaker, who recognized its occurrence 

 in "Wiltshire, Berkshire, Buckinghamshire, and Hertfordshire. This 

 author, however, regarded it as occurring between the Upper and 

 Lower Chalk ; later writers have taken it to be either the upper- 

 most bed of the Middle Chalk or the lowest of the Upper Chalk. 



The Chalk Rock fauna has been recognized at various localities 

 on the Continent. In France it occurs in the Angoumien division. 

 In North-western Germany (Westphalia, etc.) the bed is represented 

 by the zone of Heteroceras Meussianum ; and in Saxony by the 

 Scajphites-be&s, and by part of the Inoceramus Brongniarti-be&s 

 (Planer-Kalk). In Silesia the Kalk-Mergel of Oppeln belongs to 

 this zone, as do the Teplitz Beds in Bohemia, or at any rate part of 

 them. Lastly, in Bavaria the Pulverthurm Beds (the middle division- 

 of the Kagerhoh Beds) are on the same horizon. 



On account of the wide distribution of this fauna, and its contrast 

 with that found in the adjacent zones, the Chalk Rock should, I 

 think, receive a separate zonal designation ; its palseontological 

 characters are quite as striking, and far more constant than its- 

 lithological. Thus for example, at Twyford, near Winchester, as- 

 already mentioned, the zone can only be recognized by means of its 

 fossils. Moreover, so far as lithological characters are concerned, 

 the hard bed which occurs above the Chalk Rock in Buckinghamshire 

 and Bedfordshire might with equal propriety be termed ' chalk rock.' 

 If the adoption of a zonal name meet with approval, I would venture 

 to suggest the introduction of the term employed by Prof. Schliiter 

 for the same zone in North-western Germany, viz. * zone of Hetero- 

 ceras Reussianum' which for the sake of brevity might be spoken of 

 as simply the * Meussianiim-zone.' In England JScajohites Geinitzi is 

 more abundant than H. Heussianum, and would have been prefer- 

 able for use as a zonal term, but it is not quite confined to the 

 Chalk Rock. 



Although several authors \e. g. 17, 21, 26, 27, 29 of the biblio- 

 graphical list, p. 72] have given lists of fossils, no detailed study of 

 the palaeontology of the bed has yet been made. In this and the 

 following paper I propose to consider the mollusca, giving an account 

 of the synonymy and distribution of all the species, and also figures 

 and descriptions of the new or not well-known forms. In the 



