204 BULLETIN OF THE 



and arrangement. ^Narrow at the base, each joint expands so as to be 

 of a subtriangular outline in a cross section, with the exception of the 

 basal joint which is broader at the base, narrowing towards the outer 

 extrenaity. By a comparison of the longitudinal section of the basal 

 joint in Cahjniene, Plate V. figs. 1 and 3, with the transverse section, 

 Plate III. fig. 9, it is seen that this joint was transversely flattened. 

 The means of such a comparison in Ceraurus are not as good, although 

 the somewhat distorted basal joint, Plate II. fig. 6, may be placed with 

 those of Fig. 8, and compared with the transverse section of the 

 basal joint, right side, of Fig. 3. Fig. 3, Plate III., is a fine illustra- 

 tion of a section cutting across the basal joints of the thoracic legs at 

 different points, as they are brought into the line of the section by the 

 enrolment of the animal. The terminal joint of the leg has not been 

 recognized as such in either species, which makes it difficult to say 

 how many joints there are in the legs. Six is the usual number in the 

 sections, but in one there is seven, if the evidence of Fig. 2, Plate II., 

 is to be relied upon. 



The character of the appendages beneath the pygidium is one of 

 unusual interest, and for a long time was highly problematical, and at 

 present the evidence is not all that could be desired. Four sections, 

 two transverse and two longitudinal, show their presence in Ceraurus. 

 That they are jointed is shown by Plate II. fig. 8, and also in a similar 

 section not illustrated. The transverse section, Plate II. fig. 4, of the 

 extreme posterior segment of the pygidium also shows the base of the 

 leg and sections of the succeeding anterior legs. The position of 

 the base is the same as that of the posterior leg, Plate II. fig. 8. 

 That these legs were not foliaceous and branchial is evident, but what 

 their terminal joints were like is yet an unsettled problem of the 

 investigation. 



With Calymene the success in cutting a section so as to show all 

 the joints of the leg has not been as good as for Cerawus. The 

 knowledge of its structure is based on a number of fragmentary parts 

 after the third joint from the base is passed. Plate V. figs. 1, 3, and 4, 

 give a fine illustration of the first three joints. A transverse section 

 obliquely crossing an enrolled specimen cuts across the legs as they 

 diverge from the anterior extremity of the thorax. Each pair of legs 

 is cut across farther from the base, so that we have an approximate 

 outline of their form, which, from a comparison of the parts as seen in 

 many sections, resemble those illustrated on Plate VI. fig. 5, while those 

 of Ceraurus are more like those of Fig. 4 of the same plate. 



