PETALOCRINUS MIRABILIS au 
1882. Goniophyllum pyramidale Lindstrém, Palezozoiska Formationernas 
Operkelbarande Koraller, p. 43, Plates 1, 5, 6, 7, 8, 9. 
1890. Gontophyllum pyramidale. Am. Geologist, Vol. VI., p. 326. 
The presence of G. pyramidale in the Silurian rocks of America 
has not been generally recognized, the short note in the Ameri- 
can Geologist, which simply records the presence of the fossil 
in Iowa, being the only reference known to the writer. Dr. 
Lindstrém states in a communication to the writer that he has a 
single specimen of the species from Tennessee, which does not 
differ from the Swedish ones. 
Dr. Gustaf Lindstr6m has made an exhaustive study of the 
operculate corals, and he recognizes three forms of this species 
from the Swedish Silurian beds, viz., ‘ Horma primigena,” ‘‘Muta- 
tio prima,” and ‘‘ Mutatio secunda.’”’ The Iowan specimens agree 
well with figures and descriptions and also with authentic Swe- 
dish specimens* of ‘‘ Mutatio secunda”’ of Dr. Lindstrém. The 
species may be easily recognized by reason of. its peculiar quad- 
rangular form as shown in the figures. When perfectly pre- 
served the calyx is covered by four triangular valves which form 
a pyramidal operculum. A single one of the Iowan specimens 
shows one of the operculum valves in position. The specimens 
vary among themselves in the amount of curvature and in the 
depth of calyx. 
PENTAMERUS OBLONGUS Sowerby, var. CORRUGATUS, 2. Var. 
Plate VII., Figs. 1-4. 
This singular variety of Pentamerus is characterized by the 
criss-cross corrugation of the valves as is shown in the figures, 
and is apparently peculiar to this fauna. It is possible that it 
may become necessary to consider it as a distinct species, but 
as it does not differ from other variations of P. oblongus except 
in the criss-cross corrugation of the valves, and as this character 
is oftentimes faint or almost obsolete, it is thought best to accord 
to it but the taxonomic rank of a variety. 
*The writer is indebted to Dr. Lindstrom for authentic specimens of G. pyra- 
midale from Gotland. 
