NATURAL SCIENCES OF PHILADELPHIA. 
23 
very deep concave septa, and a somewhat elliptic section. Major angle of di¬ 
vergence 5° in a specimen about four inches long, giving a taper of *09 in the 
space of one inch ; ratio of axes of transverse section -98 : 1*32 = 1*34; ratio of 
concavity of septa to greater diameter *38 : 1*2 = 3*16 ; annulations, ten in the 
space of three inches, where the mean transverse axis is 1*27, making their 
distance a little less than one-fourth this axis, the plane of the annulations 
forming an angle of 74° with the longitudinal axis of the shell, the opening 
generally toward the extremity of the shorter diameter; the annulations hav¬ 
ing a broad, shallow, retral sinuosity, which in some specimens is distinctly 
marked, and in others obscure ; position of the sinuosity somewhat variable ; 
space between the annulations regularly concave ; a peculiar obsolescence of 
the annuli sometimes occurs along the side marked by the sinuosity, and not 
unfrequently a partial or nearly complete obsolescence of entire annuli takes 
place along a portion of the shell. Siphon large, situated on the longer di¬ 
ameter two-sevenths of the distance from the centre to the periphery. Sur¬ 
face (of cast) marked by feeble, rounded, encircling striae, which generally run 
parallel with the annulations, but sometimes erdss them at a small angle. 
The deep concavity of the septa is a strong distinctive mark of this, amongst 
annulated species. In many specimens this is much deeper than in the large 
specimen from which the measurements have been taken. The occasional 
obsolescence of the annulations may also be noted. 
Orthoceras heterocinctum, n. sp.—Shell unequally annulated, rather 
rapidly tapering, with a nearly circular section and a subcentral siphon. Angle 
of divergence 11° ; annulations inequidistant, strong, rounded, separated by 
concave intervals, somewhat oblique and slightly sinuated retrally on one 
of the sides, very often becoming more or less obsolete, and sometimes en¬ 
tirely disappearing; septa slightly oblique; siphon on the longer diameter 
less than its own diameter distant from the longitudinal axis of the shell. 
Surface marked by unequal strise running parallel with the rings. 
Resembles 0. Whitei in the occasional obsolescence of the rings ; and casual 
observation would not distinguish the two. The present species, however, 
tapers more rapidly, is less compressed, has a less excentric siphon and exhibits 
a much more frequent disappearance of the annuli. 
Ranges from the base of the yellow sandstones into the base of the Burling¬ 
ton limestone. 
Orthoceras Indianense, Hall, (Twelfth Rep. N. Y. Reg.,p. 10.)—Numerous 
specimens of an Orthoceras having a circular or slightly eccentric section, a 
central or subcentral siphon and an angle of divergence of about 8° fail to 
furnish any characters for distinction from the above species. If such identi¬ 
fication is correct, this species enjoyed considerable geographical range. 
Ranges from the bottom of the yellow sandstones into the base of the Bur¬ 
lington limestone, in company with crinoids regarded as characteristic of the 
latter formation. 
PHRAGMOCERAS, Broderip. 
Phragmoceras expansum, n. sp.—Shell slightly arcuate in the earlier stages 
of growth, becoming nearly straight at a later period ; somewhat gradually 
enlarging at first, but afterwards expanding with great rapidity, finally under¬ 
going a gradually reduced rate of expansion, which, at the aperture of the 
adult, amounts to a slight constriction ; transverse section very slightly com¬ 
pressed laterally; position of siphon unknown ; septa transverse, moderately 
concave. Surface of cast smooth. 
In a Specimen which is *70 in diameter at the small (imperfect) end, the 
same diameter increases to 2*1 in the space of 1*37 inches, showing an angle, 
of divergence of about 68°. 
CYRTOCERAS, Goldfuss. 
Cyrtoceras unioorne, n. sp.—Shell arcuate ; angle of divergence when young 
1863 .] 
