PLATE XLllI.— Continued. 



PAGE. 



Figs. 48 to 52. Pbimitiella CONSTKICTA, n. gen. et sp , 647 



48 and 49. Three views of a right valve; from the base of the Birdseye limestone at High 

 Bridge, KentucJjy. In this form the anterior end is rounded and the border 

 — scarcely developed. 



50. Two views of a right valve, representing the prevailing form of the species in 

 Minnesota. 

 51 and 52. Lateral and dorsal views of a longer right valve, from the lower third of the 

 Trenton shales at Minneapolis, on -which a small raised spot, situated just 

 behind the center of the valve, is barely distinguishable. 



Figs. 53 to 56. Primitiblla limbata, n. sp 648 



53. Interior of a right valve. 



54. Anterior and lateral views of another right valve. 



55 and 56. Lateral and dorsal views of a left valve. Lower third of the Trenton shales, 

 Minneapolis, Minn. 



Figs. 57 to 59. Pbimitia gibbbba, n. sp 655 



Three views of a left valve. Hudson River shales, near Spring Valley, Minnesota. 



Figs. 60 to 61. Pbimitia DUPLiCATA, n. sp ^ 654 



Lateral and ventral views of a left valve. Middle third of the Trenton shales, 

 Minneapolis, Minn. 



Figs. 62 to 65. Pbimitia TUMIDULA, n. sp 655 



62 to 64. Three views of the exterior of a left valve, obtained by an impression in gutta 

 percha from a natural mold. Hudson Eiver shales, near Spring Valley, Minn. 

 65. Cast of the interior of another left valve, from the sam'e locality. 



Fig. 66. Pbimitia UPHAMI, n. sp 651 



Three views of a right valve. Galena shales. Cannon Falls, Mionesota. 



Figs. 67 and 68. Pbimitia celata, n. sp 653 



The exterior and a ventral view of a right valve. Middle third of the Trenton 

 shales, Minneapolis, Minn. 



Figs. 69 to 72. Pbimitia micula, n. sp 653 



69 to 71. Three views of-a right valve. Galena shales, near Cannon Falls, Minnesota. 



72. Interior of a left valve, from the same locality, supposed to belong to this species. 

 The outline is somewhat different from the preceding, but there is reason to 

 believe that the valve is imperfect at the antero-ventral margin. 



Figs. 73 and 74. Pbimitia sancti pauli, n. sp 652 



Two views of a right valve. Upper third of the Trenton shales, St. Paul, Minn. 



Figs. 75 to 77. Pbimitiella unicobnis Ulrich 649 



Three views of a right valve, from the lower or Utica horizon of the Cincinnati 

 group at Covington, Kentuclty. The specimen is one of the original types of 

 the species. 



Figs. 78 to 81. Pbimitia mammata, n. sp 652 



Dorsal, lateral and ventral views of a right valve. Lower third of the Trenton 

 shales, Minneapolis, Minn. 



Figs. 82 and S3. Beyeichia initialis, n. sp 658 



Lateral and ventral views of a left valve. Middle third of the Trenton shales, 

 Minneapolis. 



Figs. 84 to 88. MooBB A punctata, n. sp 682 



A right valve. 

 Three views of a left valve. 

 '88. Another left valve In which the marginal ridge is twice interrupted along the 

 ventral border. Upper third of the Trenton shales, St. Paul, Minnesota. 



Fig. 89. MOOBEA ANGULABIS, n. sp 682 



(See also plate XLVI, flgs. 15 and 16.) 



Side and ventral views of aright valve. Middle third of the Trenton shales, 

 Minneapolis, Minn. 



