REVIEWS. 



Cambrian Geology and Palaeontology, IV, No. 7 : Notes on 

 Structure of Neolenus. By C. D. Walcott. Sraitlisonian 

 Miscellaneous Collections, Vol. LXVII, No. 7. pp. 365- 

 456 + Index, pis. xci-cv, text-figures 11-23. 

 TN this paper, the scope of which is wider than is indicated by its 

 -^ title, Dr. Walcott returns to the subject dealt with in his 

 memoir of 1918, on " Appendages of Trilobites " (reviewed in 

 Geol. Mag., 1919, pp. 359-63). Raymond's work on the same 

 subject, published in 1920 (reviewed in Geol. Mag., 1921, pp. 521-3), 

 placed a different interpretation on the appearances seen in some of 

 the fossils, and Walcott has now re-examined his material (not only 

 of Neolenus, but also of Calymene, Ceraurus, and Triarthrus) in 

 the light of Raymond's results. His conclusions are illustrated by 

 a large number of figures reproduced from photographs, for the 

 most part on a larger scale than those given in his earlier TJaper. 

 Since the reproductions, although excellently printed, fail to give 

 all the finer details visible in the original photographs, sets of the 

 more important of the latter have been distributed by the author 

 to some of the principal museums. The present writer is indebted 

 to the kindness of Dr. Walcott for a set of these photographs, which 

 are of unusual excellence and illustrate with great clearness the 

 main points emphasized in this memoir. 



Raymond's investigations led him to conclude that there was far 

 less diversity in the appendages of the various genera of Trilobites 

 than Walcott had supposed, and that the}^ were in all cases simply 

 biramous with the outer branch or exopodite bearing a marginal 

 fringe of filaments. In the case of Neolenus, Walcott had described, 

 in addition to the jointed leg or endopodite, an exopodite, two 

 epipodites, and a small " exite ", the form and position of these 

 parts being as shown in his diagram reproduced in Geol. JVIag., 1919, 

 PI. VIII. He has now again studied his material, and has also 

 submitted it to independent examination by three well-known 

 palaeontologists, Messrs. Ulrich, Ruedemann, and Bassler, whose 

 joint report is printed in this paper. They conclude that the 

 evidence for the presence of the exite and of the smaller of the two 

 epipodites is insufficient, but they agree in identifying the larger 

 epipodite, which, while resembling the exopodite in outline, differs 

 from it in details of its structure. 



Even more important are the divergences between Walcott's 

 and Raymond's interpretations of those Trilobites in which the 

 appendages are only revealed by cutting sections. In Calymene 

 and Ceraurus Walcott attributed a very complex and remarkable 

 structure to the limbs. His restorations of 1918 differed con- 

 siderably from those which he had published nearly forty years 

 earlier, but they agreed in assigning to each leg a pair of corkscrew- 

 shaped appendages regarded as gills. Raymond, while admitting the 



