S7H 
.|,;:'p„»i.ren,.l.l i. very short and thiek^ The se,.»r- 
•tkiill I / . K foninien lacerum medmin, and the aiitero- 
canal art constant and primitive characters of all 
Ihr .kull.exa.»ine.l. lastly a large laterally unossified space borders he ^ 
kail as la all nmeiit PerisstKlactyles. I have already called atten- 
tion ia the de«-riptive part ..I'lliis tneinoir to the presence of an ossthed tentornim 
in the -kail ..r »,rjae/o»/«. .is well a. to the redneed size of the hra.n cavtt.v in 
ll... Hkiill nf /-. Tlio h.w condition of the brain and the alnuKst entire sep- 
uration of it. loU-s .m‘ elmracters which indicate the low development of tl.e hnun 
ill the PahfosYophur. In Telmatolhcriiimadtridens the skull is, as far as we know, 
nitlier shorter tli.iii that of I\ pMosus, witli its vertical elevation increased. The 
ftkiill of /* cu/fridens is strongly <-oin pre.xsed, especially in the facial region. 1 he nasals 
lire cloiipitcd iiihI stmn>.dy arclied laterally, hi the premaxillary region of Telmalo- 
thfrium is foiiiiil a liiglily specialized portion of the skull ; and perhaps in P. megar- 
Atnm, when* the |»n-iiia.\ilhiry symphysis is rather more elongated and narrow than 
ill /'. fHthidosiis, we have a kiinl of transition form between the two genera in the 
pn-ianxilinry region. This is the only variation of the premaxillary region in 
/‘idtroswgs n'smiihling that of Tclmalothcrium. A very interesting character of 
the skull of Ti-lmaMhcrium is the slender and nearly straight zygomatic arch 
which agii*es in form almost exactly with that of Diplacodon. 
ExHiiuhoH of Jaio Symphysis. — The series of changes which the svmphysis of 
tile lower jaw has undergone in this scries is interesting. It commences in P. palu- 
dosMs which has a rather short symphy.sis, rounded and not horizontally jdaced. 
The diameter of the jaw lK*hin«l pivmolar 1 is considerable but the accom- 
panying table shows that it ilecrea.ses and then enlarges again in the jaw of 
/'. hvflgiMt/iu.%. In /'. ptdudosus there is no iiost-caniiie diastema but the post- 
premolar 1 iliastmna is well dcveloiied. There is a great deal of variation in the 
siw of the diastemas in F. pa/ndosus. The next step in the elongation of the jaw 
is fomnl in a small variety of Tcimatothcrium (Jaw No. 10,184). There is a decided 
elongation of the symphysis, which is more horizontally placed than in P. paln- 
dosHs. whih* c«.rn‘siH)nding with its growth there is an enlargement of the dia.s- 
temas. The |HM.t-mnnne diastema, which did not exist in P. po/itdosus, has IxToine 
well imirke,! ill this variety. This elongation of the symphysis and inorea.se of the 
diastemasis continnedin 7’. mllridcns and th rough a varietv of 7'. hyocnathus 
""'r >'io cul.ni.i- 
...... 11 . If .lie I.,..- .,1 .l,.v,.|„p„,c.,.. t.. r. I, yog, , all, u. tl.c symphysis I..., Woome 
......I. .■I..ng,...nl ,.,„| „ -kelly p,-,H-.n„lM!nt i„ position while the .liastemas 
.l.l.....fl. ... <l...l the lirs. p,x.,.,„l.,r is place.! farthoi- postei-iorlv, tl.we Ik.!,.- 
A MKMOIR WON THE GENUS 
r.l... .kull r.-i....i.. .....1 there is little variation in their |•..l-ll. 
ol tlie Skim nimio. i ^ 
the subfamily. An excei.tion to this 
