i66 Natural History Bulletin. 



Spirifera urbana Calvin.^ Plate XII, Figs, i and ia. 



The description of this species will be found in Vol. I of 

 this Bulletin, page 28. The figures on Plate XII, show the 

 outlines and general characters very faithfully, but they do not 

 exhibit the obscure plications on each side of the mesial fold 

 and sinus as clearly as they are seen in the original specimen. 



The specimen figured was found in Devonian shales, usually 

 referred to the age of the Hamilton group, near Iowa City, 

 Iowa. The species is known to occur in the central part of 

 Linn county. 



Spirifera macbridei Calvin, 2 Plate XII, Figs. 3, 3« and 3^. 



The following is the original description of this species, 

 shghtly altered: 



Shell medium size, more or less pyramidal or cyrtina-form ; 

 hinge hne equal to greatest width of shell, cardino-lateral 

 angles scarcely produced. Ventral valve sub-pyramidal, hinge 

 area very wide and slightly concave, the plane of the area 

 forming an acute angle with a plane passing between the 

 valves. Mesial sinus broad, shallow, with a low, rounded 

 ridge down the middle. Dorsal valve slightly convex, mesial 

 fold well defined, regularly rounded, protruding in front in 

 the middle line owing to the ridge in mesial sinus of opposite 

 valve. From twelve to fourteen low, rounded plications on 

 each side of the mesial fold and sinus; plications large near 

 the middle of the shell and decreasing in size towards the 

 lateral margins. Entire surface very finely granulose; the 

 o-ranules in some places, particularly on mesial fold and sinus, 

 being arranged in close-set, radiating lines. Imbricating 

 lamellae and lines of growth are crowded concentrically on 

 the anterior half of each valve. 



1 Spirifera urbana, Calvin. Bulletin from Laboratories of Natural History 

 of State University of Iowa; Vol. I, p. 28. January, 18S9. 



2 Spirifera macbridei, Calvin. American journal of Science. Vol. XXV, 

 p. 433. June, 18S3. 



