326 Reviews — Professor W. H. Hobhs — Earth Features. 



valve immediately in front of it (Figs. 11-14). This is followed by, perhaj)s, 

 two further whorls of valves with an inwardly projecting ledge, the extremity 

 of each angular ledge being fixed into the median notch of the valve in front. 

 In this manner the basal ledges join to form a flat shelf or platform extending 

 round the base of the capitulum (Fig. 116). 



The valves with a basal ledge vary in shape from an equilateral triangle to 

 one with an acute apical angle, their external basal margin being almost straight 

 and having a median notch. The basal ledge is formed by successive increments 

 in the growth of the valve, and the edges of the several laminae stand out freely 

 as sharp ridges at the base of the valve. These ledges vary in width, possibly 

 according to the position occupied by the valve, for in some of the smaller 

 valves (Fig. 10) the basal ledge is wider than in others and projects inwards to an 

 extent almost equal to the length of the valve itself. The ledge is angular in 

 shape, and, as can be seen in one (Fig. 10) or two of the more perfect valves, 

 is enlarged and slightly upturned at the apex, and is specially adapted to fix 

 into the median notch of the valve immediately in front of it. 



Much light is thrown on the inner structure and arrangement of these valves 

 by the four valves (Fig. 11) still attached to one another. The inner valve 

 (Fig. 11') without a basal ledge, but with a median notch, is one of the valves of 

 the innermost whorl, and probably occupied a position below the upper latus. 

 This is followed by two valves (Fig. 11") of the second whorl, which have an 

 inwardly projecting basal ledge ; the valve on the right hand, as can be seen in 

 the inner view (Fig. 116), is fixed into the median notch of the valve of the inner 

 whorl by the extremity of its jirojecting ledge. The third whorl is represented 

 by a single smaller valve with an inwardly projecting basal ledge, which is fixed 

 into the median notch of the valve of the second whorl. This outer valve has 

 a median notch presumably for the external attachment of yet another valve, 

 and the presence of this supports the assumption that there were four whorls of 

 valves at the base of the capitulum of this species. It is probable that the 

 valves without a median notch formed additional valves below the upper latera, 

 and in view of their structure it is difficult to conceive what other position they 

 could have occupied. One of these valves is represented in Fig. 6, and it is 

 much like the valves in the same position in the specimen of ' -B. cretacea', 

 figured by Dr. H. Woodward (1901, Fig. 4a). The four attached valves from 

 Liineburg (Fig. 11) show also quite clearly how the valves with a basal ledge 

 interlocked to form the shelf or platform round the base of the capitulum, and 

 that the bases of these valves stood almost on the same plane. The other 

 valves still attached to each other (Figs. 12, 13) probably occupied a position 

 a little to the right or left of the region below the upper latera, and formed part 

 of the first and second whorls, the valves (Figs. 9, 14) being disposed near the 

 carina, and (Fig. 8) below the rostrum, since in the specimen figured by 

 Dr. H. Woodward the lower latei'a are longest and narrowest under the carina. 



It should be borne in mind that the valves here described and figured not only 

 belong to different individuals, but to individuals in different stages of growth. 

 {To be concluded in our next Number.) 



E.E'VZE'VyrS. 



I. — Earth Featuuks and their Meaning. Ax Lntkoddction to 

 Geology for the student and the general reader. Ey 

 William Herbert Hobbs, Professor of Geology in the University 

 of Michigan. 8vo ; pp. xxxix, 506, with 24 plates and 493 text- 

 illustrations. New York: The Maemillan Co., 1912. Price 

 12.S. 6^. net. 

 rnmS volume may be regarded to a certain extent as a companion 

 JL to that on the Characteristics of Existing Glaciers (noticed in the 

 Geological Magazine for 1911, p. 569\ After introductory remarks 

 on the aims of geology and the subdivisions of the science, the author 



