Geology and Paleontology. 445 
The species Cystiphyllum davidsonii,!| which occur here in con- 
siderable numbers, also entirely replace Acervularia inequalis, of 
other portions of these beds. The Stromatoporoid forms, which. 
occur at other localities, are here replaced by a single, undetermined 
species of this genus. Specimens belonging to the following genera 
are also found here, but are not known to occur elsewhere in the 
shales. Pleurotomaria, Saxonema, Syringopora, Alveolites, Gyro- 
ceras, etc. 
_ In connection with these, we have obtained large numbers of new, 
and described, species of Lamellibranchs, which do not occur (or if 
so, in small numbers) elsewhere in this formation. mee 
ut the chief interest attaches to a certain very large, and undeter- 
mined species of Trilobite, which occurs here, and entirely replacesall 
other species of crustaceans which are known to occur at Hackberry 
and Rockford. e occurrence of this species in these beds is a 
matter of considerable interest, from the fact that it is the first in- 
stance of the known occurrence of any of these forms in the Rock- 
ford shales and indeed, in any of the Devonian rocks of northern 
owa. 
The great variation in the lithological and paleontological char- 
acters of the shales at this place, from those observed at an exposure 
one and one-fourth miles to the north, as well as those at Hackberry 
and Rockford, led us at first to doubt their equivalency. But 
subsequent collections showed a considerable number of typical 
kford shale species (as shown by the following list), which 
prove them to be equivalent to other portions of this formation,. 
as observed at other localities. The following enumeration is that, 
of some of the typical shale forms occurring here. 
Spirifera whitneyi, Spirifera hungerfordi, Atrypa hystrix, var. 
planosuleata Webster, Strophodonta reversa, Strophodonta canace, 
Campophyllum nanum, Zaphrentis solida, Cystiphyllum mundulum, 
and Naticopsis gigantea. Although the number of species repre- 
sented is considerable, yet their occurrence in individual numbers. 
are usually small. 
, , oronema gigantea, n. sp.—Shell large, cylindrical, sloping rap- 
idly from the blunt apex. Length of adult individual from ten to 
This species more closely resembles L. robusta, of Hall (15 Re- 
ts Report of New York, p. 52) than any other described species 
nown tome. It differs, however, from that species in that the 
1 This variety approaches more nearly the form from Alpena, Mich., 
aan to those from any other portion of the Devonian rocks of Iowa. 
Vapid two specimens of this species have ever been obtained (so far as. 
