Nautilus. MOLLUSCA. CEPHALOPODA. S31 
spires of the one are smooth and round, without any depression or sulci : the 
specimen is about 6 inches broad.” 
22. N. excavatus A deep central cavity ; the whorls smooth, wide, carina- 
ted, conical on the sides, and flattened or slightly emarginated exteriorly : 
chambers numerous, the syphon nearly central. The specimens which I pos- 
sess are about 3 inches in diameter, and 2 inches wide, and were given me 
by Samuel Wright, Esq., from the Carboniferous Limestone y Limerick. 
23. N. marginatus — Exteriorly carinated, sides arched ; septa waved ; sy- 
phon nearest the outer margin. In young shells the whorls are more rounds 
ed, the ridges on the back and sides being obsolete. This is probably the shell 
to which Mr Sowerby referred, at his N, pentagonus ; “ the first specimen I 
received of this Nautilus was found in black limestone, at Bathgate, Scotland, 
and given to me by my friend, Dawson Turner, Esq.” My own specimens 
collected in the same neighbourhood, appear to belong to a species different 
from N. pentagonus. In Carboniferous Limestone. 
24. N. funatus — Elliptical, discoid, volutions apparent, “ with numerous 
transverse simple rounded risings, relieved by rather wider grooves, at inter- 
vals, a kind of constriction distinguished by a small protuberance on the in- 
ner part of the rising immediately beyond it.” — Sower. Min. Conch, t. xxxii., 
where it is considered as the type of the genus Ellipsolithes. Its structure 
is unknown — In Transition LimestonOy Cork. 
25. N. compressus. — “ Elliptical, flat, smooth ; margin broad, flat, perpen- 
dicular to the sides ; volutions four or five, almost wholly exposed ; aperture 
oblong, rectangular.” — Ellipsolithes compressus. Sower. Min. Conch, t. xxxviii. 
Structure unknown, probably nearly similar to the following species, which, 
in the quadrangular form of its whorls it so closely resembles, as it likewise 
dues the N. complanatus. — In Transition Limestone, Cork. 
26. N. quadratus. — Discoid, whorls quadrangular, sides flat, smooth ; outer 
edge flat, with numerous transverse concave striae, and fine longitudinal 
ridges, four or five in number near the margin : chambers shallow, tiie sy- 
phon near the outer edge. In the cast, the outer margin is flat in the mid- 
dle, sloping off angularly to the edge ; the sides with three longitudinal 
grooves. In Carboniferous Limestone, West Lothian. 
In the four following species, the partitions have a remarkable concave 
bend on the side, making an approach to the genus Ammonita. 
27. N. ssiczac — “ Involute, inner turns concealed, aperture bluntly trian- 
gular, septa concave, much recurved at their ends with a deep indenture in the 
edge on each side, siphunculus nearest to the inside. — Sower. Min. Conch, 
t. i. lowest figure. — In the London Clay, Highgate. 
28. N. sinuatus. — “ Thick, umbilicate, concentrically striated ; side depres- 
sed, conical ; front convex ; aperture obtusely sagittate, truncated ; the septa 
have a large sinus on each side.”— Sourer. Min. Conch, t. cxciv. — In the /w- 
ferior Oolite near Yeovil. 
29. N. complanatus. — “ Discoid, compressed, smooth ; sides flat ; inner 
turns exposed ; aperture lanceolate. A reversed sinus in the edge of each 
septum, near the inner angle.” — Sower. Min. Conch, cclxi. — In Transition 
Limestone ? at Scarlet, Isle of Man. 
30. N. ovatus. — Oval, gibbose, umbilicated, edges rounded, inner volutions 
nearly concealed by the outer ; surface smooth ; aperture obtusely sagittate. 
— Ellipsolifes ovatus. Sower. Min. Conch, t. xxxvii. In some specimens in 
my possession, which I owe to the kindness of Samuel Wright, Esq., the 
septa have a deep lateral wave like the three preceding species ; the cham- 
bers are numerous, and there appear to be constrictions at intervals on the 
larger whorl. — In Transition Limestone, Cork. 
