\ f.s I 



Moor**.) 



among nliin ami Manitoba specimen-. tin- ventral c ..... lection between tin- in HIT a in I 

 filial !!:. 



Minne-ota specimens. although fri>ni a much lower hori/on than tin- types, 

 cannot be distinguished fn>m them even as a good \ariety. 



>"f>rimiri,> nn-t lofaUtg.-t.',., , MlnnonoU; upper 



llu. i- .a UiT i. 



HI Mi"i|;r:.\. -lones ami Kirkl.y. 



*"' ~ -""I KniKiiv, !> >xlll, p.4W; I88. Ann. Ma. Nat. 



nl. p. 225, and 1888, er. !,, v..|. xvn 



Carapace very small, more or \,<^ uhlnn- nr nvatc. with tin- valves 

 rather thick -helled, smooth, punctate or ^rannlo^e, ami bounded liy . 

 marginal r\>\^\ the ridge may he developed only at each end. or it may continue 

 all around. Within the marginal rid^e. the Mat or gently convex surface shows no 

 trace of a MilciH. pit. nor of Iol>e8. 



Type-: M. nl>,-s<i and M lone- and Kirkliy. 



Thi.- ^'.MIIIS i- now for the tir-t time reco^m/ed in Ix)wer Silurian mck-. and 

 twoi.f the -peeies to be de-<'ril.ed fairly illustrate the character- of the genus. The 

 third, M. '' jH-i-j, 1 . ,,f iloulitful atlinitie-. A fourth species, M. smitlin, has been 



ril>ed l.v Prof. T. linpert Jones from the Wenlock. This seems to beaquestion- 

 "'l'- the carapace being too convex and blunt at the end-, while the ridge, 



which should he snhmar^inal. is here central and bifurcated posteriorly. A fifth 

 species. M. /.-/>/%/. de>crihed from the Corniferou- limestone of Ontario by the same 

 author, i- not far removed from M. <////////r/\ while in the sixth M. /n'cornu/.i I'lrich. 

 from tlie Hamilton, the anterior end hears two spine-. M. </, I'lrich, from the 



roup of Kentuck uliar in having a granulose marginal ridge and a 



roonded subcentral itlined ly a n>w of minute papilla'. The original types 



from the Carl.onifenni- ttX iiern Knglaii-1. 



Ml tl" ies are di-tin^uished from Kirl:lj,i. .lone-, certain species of which 



they greatly roeml'ly, by the ah-eiiroof a central pit. Some also resemble Placentula 

 lones and Holl, and certain ^pei-ie- i,f /,'-,/ -he tir-t of these genera hasasmall 



dorsal loop and ,-nlcns while the latter ahvay- ha- a hor-i-hoe --haped ridge of which 

 no trace is to be observed in M The valves in the new -enn- " ',//,/ an- 



more convex and without the marginal ri 



