Dr. W. T. Caiman — The Appendages of Trilobites. 361 



show some resemblance to the pectines of scorpions, and at all events 

 the form of the elements is very different from that usually 

 indicated by the term " setae " which is here applied to them. 

 Dr. Walcott attaches considerable importance to his conclusion 

 that the limbs of the pygidium had long and slender endopodites 

 like those of the middle region of the body, and that the lobate, 

 phyllopod-like elements described by Beecher should be referred 

 to the exopodite. The photographs illustrating this point, however, 

 are not sufficiently clear to be quite conclusive. 



The revised restoration of Calymene now given differs in some 

 important details from that published in 1881. Dr. Walcott has 

 re-examined the material on which his earlier work was done, and 

 reproduces some of his figures alongside of photographs of the 

 sections from which they were drawn. As now interpreted, all 

 the limbs are provided with large gnathobases like those of 

 Triarthrus and Neolenus. In addition to the bifid spirally coiled 

 appendage, now called the exopodite, all the limbs bear a curiously 

 shaped epipodite with a terminal fringe of setae. Dr. Walcott 

 maintains his opinion that the two branches of the so-called exopodite 

 were of the spirally coiled form which he originally described, 

 rejecting the suggestion that the appearances seen in his sections 

 resulted from the cutting across of fringes of obliquely-set lamellae 

 like those on the exopodites of Triarthrus. His conclusions are 

 not to be lightly disputed by anyone who has not studied the 

 actual specimens, but some doubt must remain so long as these 

 spiral appendages have only been seen in the species examined 

 by the method of section-cutting, and not in any of the forms in 

 which the appendages are displayed in surface view. Evidence 

 has now been obtained that this species had filiform antennules 

 like those of Triarthrus and Neolenus, and they are included in the 

 restoration. 



On the much-discussed question of the affinities of the Trilobites, 

 Dr. Walcott unhesitatingly decides for their association with the 

 Crustacea, and against the view that they were related to the 

 Xiphosura and Arachnida. He does not discuss the reasons for 

 this conclusion in any great detail, and it may be suggested that 

 in the comparisons brought forward he hardly makes sufficient 

 allowance for the very wide range of structure in the Crustacea. 

 Thus, for example, it is only with large reserves and qualifications 

 that the resemblances of the Trilobite limb to the thoracic legs of 

 Anaspides can be regarded as supporting the previous comparison 

 with Apus, while it may be stated with some confidence that 

 the sessile eyes of Koonunga have nothing whatever to do with 

 the fact that the eyes of Trilobites are also sessile. Before such 

 comparison can be profitably entered upon it is essential to have 

 a clear conception of the classification and phylogenetic relations 

 of the main divisions of the Crustacea, and on this point Dr. Walcott 

 has not availed himself of the most recent information. He quotes, 

 apparently with approval, Beecher's arrangement of the Trilobita 

 " as a sub-class of the Crustacea, equivalent to the sub-class 

 Entomostraca and to the third sub-class Malacostraca ". Now it 



