DEVONIAN FAUNAS. 287 
middle, from which point it curves regularly to the margin on all sides. 
Surface of each valve marked by about forty bifurcating plications, 
which are crossed by concentric lamella of growth. 
The dimensions of a nearly perfect individual are: length, 25 mm. ; 
width, 23 mm.; thickness, 17 mm. 
Remarks.—This is a variable form, the description given being 
made to fit the more usual form of the species as it occurs at this 
horizon. ,The most conspicuous variations of the species are the 
relative convexity of the two valves, which are sometimes almost 
equally convex, and the number and size of the plications. The 
representatives of the species in the Coeymans limestone, as well as 
in the Helderbergian fauns generally, are usually more finely plicated 
than those of the Decker Ferry fauna. 
SPIRIFER CYCLOPTERUS Hall. 
Plate XXX., Wig. 2. 
See, also, p. 314, pl. XXXVIII. 
The genus Spirifer is usually not abundantly represented in the 
fauna of the-Coeymans limestone, except at the very top of the 
formation, where several species occur. ‘The commonest, and almost 
the only member of the genus in the midst of the formation, is a shell 
which has been identified as S. cyclopterus, a species which, as 
originally described, is typically a member of the fauna of the New 
Scotland beds. The Coeymans limestone specimens in New Jersey 
are all more or less fragmentary, and in none of the full-grown ones 
is the surface perfectly enough preserved to retain the characteristic, 
concentric and fimbriate markings of the species. A few small speci- 
mens, which are apparently the young of this species, agree closely 
with specimens of S. vanuxemi from the Manlius limestone, and at 
first were so identified, and some of these retain the fine surface 
markings of the species. It is possible that S. vanuawemi is ancestral 
to this Helderbergian species. 
