CBOPO 



Ar>-hln.-olU powcrl 1 



thi- type .leM-rilie.l in the following pap's, we refer)' " '"///" /n>/.//.;7ix Hillings 

 (Quebec gronpi. I/. .-nnj.!..r Hillings i '.ilciferous group), M. tr<-ntn,-nsis Hillings 

 (Trenton group) ;inl M. tatrlln Hillings (Hudson River group). 



In addition to the species of which description.- follow and those mentioned in 

 the preceding paragraph, we regard Tryl>li<liui j>ili<>luni Whitfield, T. canadetue 

 Whit eaves, Metopioin'i i>liillif>si Walcott, and M. >/</////'> Whitfield, as belonging to 

 tliis genus. 



Ai:i IHSACKLLA POWKRHI, . /). 

 3-8. 



II large for the genus, moderately convex, subovate, widest in the anterior 

 half; anterior outline semicircular, the posterior semielliptical; margins of aperture 

 r.ither -tnmgly arcuate; apex rather blunt, slightly incurved, the extreme point 

 just over the margin and at least two-thirds of the greatest hight of the shell above 

 it. Surface with fine, distant, impressed lines of growth; near the margin the 

 markings become somewhat lamellose. Length 29 mm.; width 25 mm.; greatest 

 ln^lit In mm.; hight of apex 6.5 mm. 



Impressions of the interior markings are excellently preserved on the cast 

 figured on plate \.\ I. The loop of muscular scars forms one continuous narrow band 

 curving distinctly down in front so as to pass beneath the apex. The posterior 

 third is somewhat wider and prolonged on the outer side into numerous irregular 

 processes. Within the anterior end of the loop we see the pair of rostral scars, and 

 just behind them a narrow pair lies close to the band. Finally, we observe faint 

 impressions of a larger anterior pair without the band, which may be called antero- 

 laterals. 



This fine species is readily distinguished from all described heretofore. Collec- 

 tors seem to have confounded it with A. perovalis Whitfield sp., which occurs in the 

 same strata, but is smaller, decidedly narrower in front especially and has the 

 n not quite marginal. 



Formation and JoooWy. Stone's River group. HHi.lt, Wisconsin, where the types were collected by 

 Mr. II ' !' .w.-rv rr whom the species Is named. 



a>Oeettoiu.-Unlverelty of Wisconsin; E.O. I'lridi. 



ARrHIN \rn.l.v . iN.ii'I.ATA, . gp. (I'lrich.) 



1 and J. 



Shell large, rather strongly convex. -nl>ovate in outline, very broadly roun-li^l 

 in front, more narrowly behind; hight, width and length respectively as 4.5 to 10 to 

 I'J; margin of aperture hori/ontal: apex Muntly pointed, curved downward to about 



