1923' Review. 47 



must not be too hastily assumed that P. angiistifolium is 

 a purely calciphilous moss. 



Any information or suggestion as to the possible name 

 that is hidden under the dubious " Glenlive " would be 

 very welcome, while a search for the moss in the neighbour- 

 hood of Glenariff would be highly desirable. It should be 

 looked for on rocks that are, at times at least, moist, and 

 has the appearance of a slender, small-leaved form of 

 P. alopecunim. The narrow branch-leaves with very broad 

 nerve would enable it to be recognized with the lens. 



Northampton. 



REVIEW. 



The Elasmobranch Fishes. By J. Frank Daniel. Berkeley, California ; 

 University of California Press, 1922. Pp. 334, mth 260 plates and 

 figures. Price, cloth §5.50. 



The term " elasmobranch " is applied, to those fishes whose gills are 

 plate-like in structure and whose skeleton is cartilaginous. All the sharks, 

 dog-fishes and their relations, the skates and rays belong to this group. 

 The author, who is Professor of Zoology in the University of California, 

 justly dwells on the importance of the elasmobranch fishes for the study 

 of the fundamental plan of the vertebrate body. For many years past 

 the Common Dog-fish {Scyllium catulus) which is a species of the shark 

 tribe, has been carefully examined and dissected by students undergoing 

 a course of zoology in British universities and colleges. This practice 

 does not seem to be carried out to the same extent in the United States, 

 and Prof. Daniel endeavours by the publication of this book to rouse a 

 more general interest in the study of elasmobranch fishes. 



There can be no doubt about their being a very primitive group of 

 fishes. Comparatively few species are still hving. But in bygone ages 

 there existed many more, and some of them attained gigantic proportions. 

 Many of the extinct forms are only known from their teeth which have 

 been preserved to us in various geological deposits. 



One of the most interesting types of Elasmobranchs is Heptanchus, 

 a shark possessing no less than seven gill-shts and the same number of 

 gill-arches. Together with Hexanchus, to which it is very closely related 

 and which occurs in Irish waters, it has often been placed in the genus 

 Notidanus. It is this genus Heptanchus which, on account of its special 

 generahzation, has been chosen by Prof. Daniel as a type with which to 

 compare in general other elasmobranch fishes. It inherits more than 

 any other shark the main features of its remote ancestors. The author 

 has also collected and combined the work done by many investigators 

 on the various types. 



