Reviews — Geological Survey of Illinois. 321 



median ridge (Fig. 2, m.) of the equine tooth, yet we think that 

 this is foreshadowed in the former by the flexure which often 

 occurs in the ectoloph between the para- and meta-cones. 



In referring to the secondary enamel-folds which grow from the 

 three compound elements of the Ehinoceros molar into the median 

 valley (the large fissure penetrating Fig. 5 from the inner side), it 

 is to be regretted that Prof. Osborn has again displayed some care- 

 lessness in quoting previous work. Thus he states, "These secondary 

 elements consist, first, of three folds projecting into the median 

 valley, one from the ectoloph, the crista ; one from the protoloph, 

 the crochet ; one from the metaloph, the anticrochet ;" his figures 

 being lettered accordingly. Now the fact really is that it is the 

 crotchet (as we prefer to spell the word) which projects from the 

 metaloph, as shown in Fig. 5, while the anticrotchet, when present, 

 is carried by the protoloph. The crotchet corresponds, in fact, pre- 

 cisely in position with the projection arising from the protoconule 

 of the protoloph of the equine molar (Figs. 3, 4) ; and when reaching 

 across to the metaloph divides the median valley into an inner and 

 outer moiety precisely after the equine manner ; the only difference 

 being that while in the Ehinoceros the two divisions of the valley 

 remain open, in the Horse they are completely filled with cement. 

 (In Fig. 3 the cement filling the * island ' formed by the outer part 

 of the median valley is drawn white, while that in the outer part 

 of the same — between pr. and ml. — is made dark and crossed by 

 vertical lines; this difference is owing to the staining of the fossil, 

 but in a recent Horse's both would be pale buff.) 



In conclusion, it may be observed that, while it may be convenient 

 in monographs to retain for the description of the molars of the 

 various families of the Perissodactyla the terms commonly in use, 

 yet the importance and interest of being able to trace the precise 

 morphological equivalents of the elements of all these teeth, not 

 only to one another, but also to the primitive type of mammalian 

 tooth-structure, can scarcely be overrated. To a certain degree as 

 regards the former part of this task, and altogether as regards the 

 latter part, zoologists and palEeontologists are indebted to the labours 

 of Prof. Osborn. E. Ltdekkek. 



II. — Geological Survey of Illinois, A. H. Worthen, Director. 

 Volume VIII. Geology and Paleontology. Edited by Josua 

 LiNDAHL, Ph.D., State Geologist. Geology, by A. H. Worthen. 

 Paleontology, by A. H. Worthen, Charles Wachsmuth, Frank 

 Springer, E. O. Ulrich and Oliver Everitt. With an Ap- 

 pendix [Biography, Bibliography and General Index to Volumes 

 I.-VIIL). Text. Published by authority of the Legislature of 

 Illinois, July, 1890. 8vo. pp. xiii. 758 and 151, 1 Portrait, 

 1 Map. Plates I. — LXXVIII. and Explanations, bound in a 

 separate volume. 



WITH this massive volume and the Plates accompanying it, 

 the series of Eeports on the Geology and Palaeontology of 

 Illinois, which have appeared at various intervals since 1866, is 



DECADE III. — TOL. VIII. — NO. VII. 21 



