CEPHALOPODA. 41 1 



Nautilus liratus, var. juvenis, n. var. 



PLATE LVI, FIGS. 5, 6. 

 Nautilus liratus, Hall (in part). Illustrations of Devonian Fossils : Cephalopoda, pi. 57, figs. 5, 6. 187G. 



Shell subovoid, discoid. Transverse section elliptical. The ventro-dorsal 

 diameter about three-fifths as great as the transverse diameter. A part of 

 the difference being probably due to moderate compression. 



Volutions rapidly expanding from near the base of the great cham- 

 ber, which is subovoid, with unequal diameters. Number of volutions 

 unknown. 



Chamber of habitation deep and wide, having a length, on the convex side, 

 of fifty-five mm., with an equal transverse diameter at the aperture, and a 

 ventro-dorsal diameter of twenty-eight mm. Aperture transverse to the 

 direction of the tube, elliptical in outline. Ventral side entire, without sinus. 

 Air-chambers not satisfactorily determined : there are about four attached 

 to the base of the grand chamber, which are partially crushed and the form 

 distorted. 



Septa direct, moderately concave. Suture lines not satisfactorily observed. 

 Siphuncle obscure, apparently small and subcentral. 



Test thin, imperfectly preserved on the specimen. Surface, in the partially 

 preserved shell, marked on the concave and lateral faces by slender, sharp, 

 cariniform ridges, of which there are fourteen or fifteen on each side, 

 becoming gradually subdued and obsolete on the convex or ventral side. 

 Ventral side marked by about twenty subdued, rounded, longitudinal striae, 

 which are arranged at subequal distances on each side of a wider median 

 space. Entire surface marked by fine, even, transverse, thread-like striae, 

 which traverse the flat or concave interspaces, and arch over the ridges, 

 producing a crenulate aspect. On the ventral side these transverse striae 

 are more conspicuous than the longitudinal striae, which do not perceptibly 

 interrupt their course. The surface is farther marked by low, rounded and 

 inconspicuous, transverse undulations, of which about eleven may be counted 

 on the grand chamber. No sinus has been observed in the margin of the 



