Nautilus. MOLLUSCA. CEPHALOPODA. 231 



spires of the one are smooth and round, without any depression or sulci : the 

 specimen is about 6 inches broad." 



22. N. earcavatus 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^ Limerick. 



23. N. marginatus Exteriorly carinated, sides arched ; septa waved ; sy- 

 phon nearest the outer margin. In young shells the whorls are more round- 

 ed, the ridges on the back and sides being obsolete. This is probably the shell 

 to which Mr Sowerby referred, at his N. pentagomis ; " 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. fiirtatus 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 EUipsolithes. Its structure 

 is unknown. — In Transition Limestone, 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." — EUipsolithes 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 

 does 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, the 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. siczac " Involute, inner turns concealed, apertiu'e 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. — Soiver. Min. Conch. 

 t. L lowest figure In the London .Clay, Highgate. 



28. N. sinuatus.—'-'- Thick, umbUicate, concentrically striated ; side depres- 

 sed, conical ; front convex ; aperture obtusely sagittate, truncated ; the septa 

 have a large sinus on each side."— Sower. Min. Conch, t. cxdv. — In the In- 

 ferior Oolite near YeoviJ. 



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." — Soiver. Min. Conch, cclxi. — In Transition 

 Limestone'^ at Scarlet, Isle of Man. 



30. N. ovatus. — Oval, gibbose, umbiUcated, edges rounded, inner volutions 

 nearly concealed by the outer ; surface smooth ; aperture obtusely sagittate. 

 — Ellipsolites 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. 



