10 [359] A Wincliell on supposed New Cephalopods. 
(Proc. Acad. Nat. Sci. Phil., Jane, 1861, p. 147; and this Jour., 
[2], xxxii, 174). N planidorsails bears an extremely close re¬ 
lationship to N. digonus , Meek and Worthen, from the Rockford 
“Goniatite bed” in Indiana (Proc. Acad. Nat. Sci. Phil., Oct., 
1860, p. 470). It differs, however, by having a very distinct 
longitudinal groove along each lateral boundary of the dorsal 
area, and extending apparently the whole length of the shell, 
while N. digonus “is marked by two very obscure lateral depres¬ 
sions near the aperture.” N digonus also is “ rounded regularly 
into the umbilicus,” from the angle which bounds the dorsal 
area, while in N. planidorsalis ) the “regularly rounded” area is 
separated from the dorsum by a dorso-lateral area which is con¬ 
cave. 
Nautilus (Trematodiscus) trigonus, n. sp. 
Shell of moderate size, rapidly enlarging, marked longitudi¬ 
nally by three prominent, obtuse angulations—one dorsal and 
two dorso-lateral. The dorsal ridge is broadly convex, but the 
nature of the specimen does not permit me to ascertain whether 
or not the center is marked by a narrow groove. The dorso¬ 
lateral ridge is also regularly curved, and a small concave fur¬ 
row separates it from the dorsal one. The slope from the dorsal 
to the dorso-lateral ridge makes an angle of about 65° with the 
dorso-ventral diameter. A broad, shallow lateral furrow suc¬ 
ceeds the dorso-lateral ridge, and this is followed by a regular 
convexity descending into the umbilical cavity. The transverse 
diameter through this convexity is scarcely greater than that 
through the dorso-lateral ridges. The surface (of the cast) is 
smooth. The septa are rather deeply sinuous—a strong sinus 
turned backwards, occupying the dorsum, and a deep broad 
sinus, the side, these two being separated by an abrupt saddle 
whose apex rests upon the dorso-lateral keel. 
Measurements , of a fragment forming less than half a volution, 
wholly septate. Dorso-ventral diameter *45; transverse diame¬ 
ter about *54; distance from dorsal to dorso-lateral ridge -18; 
depth of dorsal sinus *07; of lateral sinus T4; interseptal dis¬ 
tance on the dorsum T7. 
Locality. Marshall. 
Nautilus (Trematodiscus) striatulus, n. sp. 
Shell small, rapidly enlarging, whorls not impressed, flattened 
on the dorsum on each side of the peripheral line, and thence 
rounded regularly into the umbilical expanse; transverse sec¬ 
tion somewhat elliptic, with the major axis corresponding to the 
transverse diameter of the shell. Septa slightly sinuous, one 
broad shallow sinus extending across the side and another across 
the dorsum. Surface finely and elegantly fluted longitudinally. 
The largest fragment of this species is about half a volution, 
