I'l.ATi: I. XI 



Figs, land 2 AKI HIN Pitt 



I> <rsal and proii: . -hell of this specie*. Black River group, 



Menvr cniifit>, Kentucky 



A KI in-. . OH RRSI U. an ! - 829 



3 ami 5 Tronic and dorsal views of a cawt of tho Interior showing muscular ImpreMlont In 

 a very *atlsfact..r> manner. A, rtMtral scare; B, antero-laterals; C, the loop: I), 

 a narrow pair living Just within tli< ' p Stones River group, Belolt. U 



i. I'nlverslty of Wisconsin 

 4 Ik.r-iiui of same nhell as shown by agutta percha Impression of Its matrix. 



Flga. and 7 AIK-HIN M n.i v i;n HMUNPKN-I* Ulrlch 834 



Dorsal and profile views of a gulta percha Imprewion of the exterior of the shell 

 whlrh was overgrown by a bryocoan and subsequently dissolved away. Rich- 

 mond group. Richmond, Indiana. 



Figs. ( and 9 Au< HIV v KI.I \ OKI-KRMA U. and S 830 



Ifcinuil and profile views of the type <>f this species. Stones River group, Minne- 

 apolis, Minnesota. Geological and Natural History Survey of Minnesota, Mu- 

 seum Register No. 56S3. 



Klgs. 10 ami II Am U IN ix U. and S 833 



1'r. !',:. ami dorsal views of a cast of the exterior from tho Phylloporlna bed of the 

 Black River group :tl .St. Paul, Minnesota. 



Figs. 12 and i:t AK< HINACKLLA SEMICARINATA U. and S 833 



Two views of a cast of the Interior, showing the carlnate umbo and usual form of 

 ^pecles. The linear muscular loop Is faintly Indicated. Clltambonlteii bed 



of the Trenton group. Cannon Falls, Minnesota. 



Am it IN v KI.I. v \ AI.IIIA Sardeson sp 832 



Two views of a rathersmall specimen of this species. Trenton group (Clltambon- 

 Ites beds), Cannon FnlN. Minnesota. Geological and Natural History Survey 

 of Minnesota. MH-. um Register No. 7417. 



Figs. 16 to 20 AKCIIINACEI.I.A DELRTA Sardeaoo sp 831 



18 and 20 Two views of an unusually narrow specimen, from Minneapolis. This, like the 

 original of figures 18 and 10, grew upon the Inner surface of a spiral shell. A 

 part of the Internal cast of the latter now forms the under side of the specimen 

 and gives It the appearance of a blvalved shell. 



17 A specimen of the usual size and proportions. Goodhue county, Minnesota. 

 18 and 19 Two views of a wide cast of the interior. Near Fountain, Minnesota. Geological 

 and Natural History Survey of Minneftota, Museum Register No. 4087. 

 All from tin- Ctenodonta bed of the Black River group. 



Flga. 21 to 23 AKf niNAiKi.i.A iNsTAHiLi* var. INCUK\ A U. and S 835 



Three views of an Imperfect specimen of this variety, the Orst of the natural size, 

 the ..UMTS magnified. Ctenodonta tied of the Black River group, Goodhue 

 county, Minnesota. 



Flga. 24 and 2& Au> IIINACKI.I.A ROTUNDA D. and S. 835 



Two views of the cast of the Interior upon which this species Is founded. The 



inner l-.nl. r of the continuous muscular loop Is sharply preserved, but the 



me point of the rostrum and part or the margin on the left side Is wanting 



In the spiTtriien. I'tii-a ifroup, Graf, Iowa. 



Figs. 28 and 27 AK< m. - *34 



IT..II:.- and dorsal views of an entir- shell of this species. Ctenodonta bed of the 

 Black Itiver group, near Cannon Falls, Minnesota. 



I 28 IlKU ION S-ATK IV :iml > 827 



Dorsal view of a partial cast of the interior of this species. The upper line repre- 

 sents the appearance of this part <>f the outline In another specimen. The radi- 

 ating lines In the right uj>i-r fourth of the figure probably represent muscular 

 Imprints. Betw.^-n th-se ami the margin the specimen shows numerous very 



fine radiating lines, which we believe Correspond with lines upon tl xternal 



surface of the shell. The profit- -arly as in figure 20 of this plate. Cll- 



tambonltes bed of the Trenton trroup, Goodhue county, Minnesota. 



