734 



itEroRT — 1884. 



Ponnsylvanin. 'I'liis shnln in New York immcdifttdy ovorliuM the Ninpaia liinp. 

 stone, which is corrohited on suti.sfacturv evifleiice witli I lie Weiilock liiiicsiouc of 

 J'lnf^hiiid. Ten or twelve species are coimiioii to the two hculs. 



II seems, thoreforo, that the <rrtjat mass of coloiirert shale, near tho top of which 

 these fossils were found, and which isa continuation of the Onondapja jrroup of Xcw 

 York, has no representative in the Ihitish series, hut corresponds to nn iiiterxnl 

 hetween the Upjier Wenlock and the iiower Ludlow. (For di^tails reirardin;,' thu 

 correlation of these l)eds in Pennsylvania with tlio^e in New York, see a pajier by 

 the author in ' Proc. Amer. i'liil. Soc.' for IFHi.) 



It is consequently a necessary inference lliat the bedb yieldinir I'dhcd^spix and 

 Oiichns in Pennsylvania are somewhat older than those containini,' SfdithuHpiK ami 

 O/irkus in lOn^dand. 



Microsco))ic examination of the specimiMn, and a coniparisr)n of their stnicturp 

 with that of iScti/ifia.iin's and Vrp/i(ilii.i/)i.s, nr(: in progi'ess, and tiie details will jn' 

 •jiven l)elow. Other fossils in the autlior's possession indicate tlie ])ossihle exisl- 

 •ence of lish at a still earlitu' date, hut tlie material is not yet worked out. 



The microscopic structure of I'dhciispis corresj)onds in all important points witJi 

 that of ScaphdspiH as tij.'ured hy Huxley ('(^ J. (J. S.' vol. \iv., pi. xv.,fig. 1), Tln' 

 basal cellidar and vascidar layers are ]iresent in both, but the hitter presents n 

 reirnlarity of struct ur(( to which Scniihaxpii^ alfords no ])arallel. A section parallel 

 with the striatiou presents a beautiful forest-like ap))earance produced by the Hm' 

 and diver<rence of the tubules from the larger ve,s.sels. The most reniarkulJi' 

 anatomical peculiarity f)f these fossils is also one in which the^^ coincide with the 

 Pteraspids of I'hi^'land. All the spi'cies belon'j-injr to this j^ronp are dislinjrni.slinl 

 by the total absence of the hone cells (Incinin ) and the connecting' tiihules [rami- 

 liculi) characteristic of all other bone-structure in all class<'S of the animal kiuff- 

 dom. This absence was tiie {rreatest objection to the admission of the Inssil tu 

 this class of lishes. Thou|.'h now overruled, Us importance is in no wise diminished. 

 To receive these ftn-ms the ^nuip of Iletei'ostraeans was established by Proje.^^sov 

 Lankester in l8(ii( as a sub-division of Huxley's fauuly of (Vphahispids. ' So'pro- 

 fonnd a dillerence, however, formini,' a distinct line of demarcation between thr 

 fossils of the family seems to demand bolder recofjrnition, and it was ^iroposod tn 

 raise Lankester's sub-family of Ib.'ten stracans into a distinct family under tln' 

 name of Pteraspids {l^eran/mlw) and the name of Cephalaspids {C'ep/ialas/iula) he 

 retained for thost; forms exhibiting' true bony tissue, and composing the suh-fumib 

 of the Osteostracaus of Jjankester. 



3. 0)1 jUnerican Jurassic Mammals. Bij Professor 0. C. M.vrsh. 



The first Jurassic ^rammnbs discovered in this country were found in ]8"8, in 

 the Atlantosaurus beds of Wy^ininp- Territory, and described by the author. Other 

 discoveries in the same region soon followed, and a systematic exploration of this 

 geological horizon has been c(nitinued by the author uj) to the present time. 



This horizon in the upper Jurassic, with its characteristic fossils, has been 

 traced by the author along the ilanks of the Itocky Mountains for a distance of 

 more than three hundred miles. Its position is shown in the geological .section on 

 page 7;i'). The deposits are lacustrine, and the accompanying fossils are dinosaurs, 

 pterodaetyles, crocodiles, lizards, and iishes. 



Remains of Mammals have been found by the author at several points along 

 the line of this horizon for two hundred miles or more, hut the most productive 

 locality is in the region where the first discovery was made. At one point, from 

 41 space scarcely larger than the room in which the author was speaking, remains 

 ■of more than three hundred individuals of Jurassic Mammals have been obtained, 

 a good indication of the wonderful richness of the fauna here entombed. 



Other localities have yielded many important specimens, so that up to the pre- 

 sent time, the author has secured the remains of nearly or (juite four hundred 

 individuals of Jurassic Mammals. So far as known, no other specimens of this class 

 have been secured from this formation in America. 



