Geology and Paleontology. 1101 
tinct false mesial sinus in the ventral valve. Several other varie- 
ties of this species also occur in different portions of the State. 
Not only do the Iowa varieties of this species vary greatly in 
form, size and surface markings, but they also often differ conspic- 
uously in their internal structure. Some forms of this species ap- 
proach so near to Atrypa impressa of the Schoharie Grit of New 
York, that a strict distinction between them is impossible. Atrypa 
reticularis of the Iowa strata varies so much in form, size, surface 
marking, etc., that it could be separated into several forms suffici- 
ently distinct to have specific names, if the forms were found only 
distinct groups of rocks. Atrypa hystrix and Atrypa aspera also 
vary greatly in form, size and internal structure. An interesting 
feature of the Brachiopod and Polyp faunas of the Devonian 
strata of Iowa, is the occurrence of quite a number of forms which 
imperceptably grade into one another; but which forms are seen, 
in the rocks of other States, to constitute well-marked species. This 
condition is more particularly noticeable among some forms of the 
genera Favosites, Cyathophyllum, Atrypa and a few others. 
spirifera substrigosa, n. sp.—Shell a little larger than medium, 
somewhat longer than wide, slightly gibbous; cardinal extremities 
abruptly produced into short rounded projections. Dorsal valve 
moderately convex; greatest convexity slightly above the centre. 
Mesial fold angular, strongly produced in front; mar y five 
small scarcely elevated rounded plications, only one of which 
reaches the beak. Valve, on each side of the mesial fold, marked 
by five strong, broadly rounded radiating plications; cardinal ex- 
tremities smooth. Ventral valve rather gibbous; greatest convex- 
ity about the centre; mesial sinus rounded, of moderate depth, quite 
rapidly expanding below, and produced into a moderately road 
rounded extension; beak much elevated, sharp and strongly in- 
curved ; foramen rather large, triangular; area moderately large, con- 
cave. 
Surface of the ventral valve, on each side of the mesial sinus, 
marked by six or seven strong, rounded, radiating plications; a _ 
small area on the cardinal extremities smooth. esial sinus orna- 
than to any other described species known to me. Position and 
locality: Rockford Shales, Hackberry, Iowa. me me 
Spirifera hungerfordi Hall. (Compare with original description, 
Geo ogy of Iowa, Vol. I, Part 2, p. 501.)—Shell very variable, 
adult forms often being three and one-fifth centimeters in width, 
