98 PALEONTOLOGY. 



CEPHALOPODA. 



GONIATITIDiE. 



aenus GONIATITES, De Haan. 

 GoNiATiTES GONiOLOBUS, Meek. 



Plate 9, figs. 5, 5 a, 5 h. 



Shell distinctly discoid, with (in internal casts) a narrowly-rounded 

 periphery; volutions compressed laterally, with slightly convex sides, the 

 greatest convexity being a little within the middle; about twice as wide in 

 the dorso- ventral diameter as at right angles to the same; each turn em- 

 bracing all the others, so as to leave only a very small umbilicus, showing 

 none of the inner volutions. Septa closely and very regularly arranged, 

 but nowhere in contact or lapping upon each other; siphonal lobe (gener- 

 ally called the dorsal lobe) very large, and profoundly divided into two 

 large, elongated, acutely-pointed terminal branches, which lap so far over 

 each side of the volutions as to appear each like a large lateral lobe; 

 while between these there is a third minute central projection; first lateral 

 sinus very deep, elongate-conical, very acutely angular at the extremity, 

 and arched or obliquely curved toward the umbilical side; second lateral 

 lobe of much the same form as the divisions of the siphonal lobe, but a little 

 shorter; second lateral sinus wider than the lateral lobe, but more shallow, 

 and merely forming a broad forward arch to the umbilicus. Surface of 

 internal cast without nodes, costse, or angles. 



Greatest diameter of a specimen, with the body-chamber broken away, 

 3.07 inches; convexity, 0.87 inch; breadth of outer volution, measuring in 

 the direction of the plane of the shell, 1.72 inches. 



Excepting in being more compressed, with a more narrowly rounded 

 periphery, this species has much the general appearance externally of G. 

 rotatorius, De Koninck. Its septa are more closely approximated, however, 

 and differ remarkably in having the siphonal lobe so enormously developed, 

 and so wide and deeply divided as to lap over on the sides far enough to 

 cause its large, acutely-pointed terminal branch on each side, to appear, in a 

 side-view, like a first lateral lobe; while the first lateral lobe is thus, as it 

 were, crowded much farther inward, and appears like a second laterf.1 lobe. 



