ON THE CARBONIFEROUS XIPHOSIJROUS FAUNA. 147 



from the otiicrs in (Ending abruptly, tlie p(Muiltiiuate Joint beiii;^- lon^ and of the same width 

 throughout, and truncate at tlie distal end, where it gives rise to three small, sharp sjiines ; there 

 are also traces of a terminal minute joint from which two spines arise. 



Length of second, tuird. fourth, and fifth pairs of legs, 16">"'. 

 Length of sixth pair, 17""". 

 Length of pennltlniate. joint, 6""". 

 Thickness, 1""". 



The legs are nearly identical in shape and length with those of the larva of Limulus described 

 and figured in my Development of Limulus (PI. 1, figs. 24% 25*, and 23''), though perhaps a little 

 shorter, as they do not reach beyond the edge of the cephalic shield. It thus appears that in 

 respect to its limbs as well as the shape and proportions of the bodj^ the Prestwichia resembles 

 the larval Limulus. Thus Limulus in its development passes through a trilobitic, and afterwards 

 a Belinurid stage. 



Prestwichia longispina Packard. PI. V, fig. 4. 



Kiii)ro(}i)n JonijiapUui Pack., Amer. Naturalist, xix, iJ92. March, 1885. 



The specimen upon whicli this species is founded is Mr. Lacoe's Nos. 215'*'' (impression and 

 reverse), and was probably a molted skin (PI. V, fig. 4). The body is considerably distorted by 

 pressure, but the specific distinctness from P. danw is marked. The species will be readily dis- 

 tinguished by the very long genal spines; they extend nearly or quite to a point opposite the base 

 of the caudal spine. The abdomen appears to be narrower in proportion to the cephalic shield 

 than in P. daiuv while the genal spines are longer and narrower. The caudal spine is not well 

 preserved. 



Length of body (not including the caudal spine), 20™"'. 



Length of head, 10'>>'". 



Length of abdomen, 10"'". 



Breadth of cephalic shield, 24""". 



Breadth of abdomen, 13""". 



Length of lateral cephalic spine, 13"'™. 



Pittstou, Pa., Butler mine, Nos. 215*'', collection of Mr. Lacoe. 



In another larger specimen (Lacoe's No. 214", PI. VI, fig. 3), the glabella, with the eyes, ocelli, 

 and a part of the left lateral spine are preserved. Whether this is the same species as P. lo7igispina 

 I caanot tell with certainty, as the genal spines are not sufficiently well preserved, but'provision- 

 ally it may be regarded as belonging to the species under consideration. The median lobe of the 

 head is larger in proportion to the entire cephalic shield than in P. dawe, and the eyes are nearer 

 the lateral margin. The ocelli are situated on the median ridge of the lobe, somewhat behind the 

 indentation between the lobes. The individual is without doubt a Prestwichia having the same 

 number of abdominal segments as in P. dame. 



Length of body (without the caudal spine), 30""". 

 Breadth of cephalic shield (estimated), 37""". 

 Length of cephalic shield, 17-18'"'". 

 Length of abdomen, 13'"™. 

 Breadth, 23™™. 



Estimated length of lateral cephalic sjiiue, l.^""". 

 Distance between the compound eyes, 17™™. 

 Distance from ocelli to the front edge of body, 6""". 

 Distance from ocelli to hinder edge, 21™"'. 



Oakwood Colliery, Wilkes Barre, Penn., collection of Mr. Lacoe, No. 214*. 



Regarding the position of the Illinois and Penn.sylvania beds containing these fossils, Mr. Lacoe 

 ■writes me: "The horizon of the Pennsylvania specimens of Euproops is much higher than that of 

 Mazon Creek. The latter is at the very base of the productive coal-measures in shale over the 

 bottom seam of coal. The specimen from the Butler mine, Pittston, is from shale over coal 'PI' 

 (Mammoth vein), at the top of the lower productive coal-measures, about 300 feet above, and that 

 from the Oakwood colliery is either from the same horizon or the bottom of the lower barren 



