18V0.J 



BTT.MVns — LOWEH-SIIiURIAJr 'rKiXOnn'KS, 



485 



2. No fossils of the order ( Xlphosura) to <vhiih Limulus belongs 

 havi' been found so low down as the I'otsdain siuidstoue. 



'». Largc^ Trilohitos occur there in ubuiulanco. 



riio wei^iht of the evidence, tlierefore, favours (he 'nion that 

 the tracks in (jncHtion are tho le of Trilobites. It is important to 

 bear in luind that I'rotii'hniteit and Cluiiactlchnites occtxr togdlie'" on 

 the hanie slabs of i^and-itoue. Dr. ])a\vson's observations, clearly 

 prove that both might havf been made by an animal of tho same 

 species under ditFcrciiit circumstances, accordingly as its walking- or 

 its swinmiing-feet were made use of. Judging from tho width of 

 the tracks, 1 b(;lit>vc that several of those of both kinds oji one of the 

 slabs, now in the Muaeuui of the Survey, were made by the same 

 imlividual. 



4, On a roUed-up specimen o/Talymone scnaria^Z^^c? mlh small 



ovate fiodii's. 



It is above stated that whde seeking for additional evidence re- 

 lating to the limbs of 'frdobites, a number of specimens were cut up 

 and jxilished. One of these was an exceedingly perfect, rollcd-np 

 CaJiimene senaria, from the Hudson-lliver group at Cincinnati, in 

 Ohio. 



This animal (PI. XXX 11.. fig. H) appears to have shut itself U]» so 

 coin[)lett'h' that the fine mud in wiiich it was buried could only 

 gain access througli the small fissure at </, where tho points of the 

 head and tail come together. There is here a small space, within 

 the letters, c, d, e, f, which is of a light j-ellowish brown. 1 think 

 that neither the mud, iu>r even the muddy water, penetrated fur- 

 ther. There is ni» trace of comminuted fossils in this space, as there 

 is in moat specimens that 1 have cut up. The whole of the re- 

 mainder of the cavity is tilled with a greenish-grey spar, with a 

 patch in the back part of the Jiead at h of a ditFerent colcmr. This 

 Bpar holds a vast number of small ovate bodies (fig. 4), of which the 

 greater diamet(>r is about an eightieth of an inch, and the lesser a 

 hundredth. They ar(.i of a lighter colour and more opaque than tho 

 matrix. When examined with a good glass, and under favourable 

 light, they seem to float, as it were, in the spar. The hypostoma 

 c d, is in places and is here cut through. From the end of the tail, 

 at e, a thin rough line runs inwards, nearly to the large spot at /, 

 and is obscurity indicated thence to the end of the hypostoma 

 at c. The spot /' appears to be organic. It is of an ovate form, 

 and has four or five obscure ribs across it at right angles to its 

 greater diameter There are other dark spots scattered irregularly 

 throughout the matrix, that possibly may represent organic struc- 

 tures. 



It is possible that the line e fe may represent the edge of the 

 ventral integument cut through ; for in a rolled-up trilobite this 

 must be exactly its po.sition. The small ov.ate bodies I beli ? to 

 be the eggs. 



