Br. W. T. Caiman — The Appendages of Trilobites. 359 



III. — Dr. C. D. Walcott's Besearches on the Appendages op 



Trilobites. 

 By Dr. W. T. Calman, D.Sc, F.Z.S., 

 of the British Museum (Natural History). 

 [Dr. C. D. Walcott. Cambrian Geology and Paleontology, IV, 

 No. 4 : Appendages of Trilobites. Smithsonian Miscellaneous 

 Collections, vol. lxvii, No. 4, Washington, December,- 1918, 

 pp. 115-216 -f- Index, pis. xiv-xlii, text-figs. 1-3.] 

 (PLATE VIII AND TEXT-FIG. I. 1 ) 



IT is nearly forty years since Walcott published the well-known 

 memoir which first gave palaeontologists definite information 

 regarding the appendages of Trilobites. This -work was based on 

 a laborious investigation of Calymene senaria and some other 

 species by means of thin sections. Since then much knowledge has 

 been gained, and, in particular, Beecher's researches on Triarthrus 

 have provided us with a new conception of the Trilobite limb 

 which, in some respects, is not readily to be reconciled with 

 Walcott's earlier results. Now, at length, in this finely illustrated 

 monograph, the veteran student of the Trilobita brings together the 

 results of his own work and that of other investigators and reviews 

 the whole in the light of his unrivalled experience. 



In all, eleven species are dealt with, and restorations are given 

 of Calymene senaria, Triarthrus becki, and Neolenus serratus, the 

 three species of which the structure is most fully known. The 

 last-named species is represented by finely preserved specimens 

 in the Burgess shale (Middle Cambrian) of British Columbia, from 

 which Dr. Walcott has described so many novel forms of animal 

 life in recent years. 



By the kindness of Dr. Walcott we are able to reproduce two 

 of his figures illustrating Neolenus (see Plate VIII and Text-fig. 1). 

 It will be seen from the restorations that the limbs are of some 

 complexity. The jointed and spinous leg (endopodite) has a strong 

 basal segment, produced inwards as a toothed gnathobase, to which 

 are attached as many as four lobular appendages. One of these, 

 distinguished by the marginal fringe of long seta?, is identified as the 

 exopodite, and two others, one large and one smaller, are lettered 

 as epipodites. Another small lobe is called an " exite", but as it is 

 stated to be "probably attached to the inner side of the protopodite " 

 the name is hardly well chosen. The most remarkable feature of the 

 species, however, is the presence of a pair of long multiarticulate 

 caudal filaments resembling those of Apus. Nothing like these has 

 hitherto been seen in any Trilobite (Text-fig. 1, c.r., p. 360). 



In the case of Triarthrus the modifications which Dr. Walcott 

 finds it necessary to make on Beecher's well-known restoration 

 are mostly of a minor kind. The chief is the addition of a series 

 of small leaf-like epipodites attached to the bases of the limbs. 

 The fringes of the exopodites were described by Beecher as made 

 up of "narrow, oblique, lamellar elements", and he suggested 

 that they may have served as gills. The photographs now given 



1 The original illustrations have been kindly lent by Professor CD. Walcott. 



