CEPHALOPODA. 383 



Air-chambers regularly increasing in depth from the apex to the grand 

 chamber, varying from two to eight mm. in the length of nearly fifty air- 

 chambers. In larger specimens the chambers have a depth of eleven mm. 

 toward the grand chamber. Septa smooth, having a concavity equal to the 

 depth of the air-chambers. Sutures straight and at right angles to the spiral 

 axis of the tube. 



Siphuncle ventral, nummuloid, small in its passage through the septa, and 

 very much and abruptly enlarged in the cavities of the air-chambers, assum- 

 ing the form of flattened, ovoid expansions between the septa, which have a 

 diameter equal to the depth of two air-chambers. 



Test thin, having a thickness of .5 mm. on the outer volution. Surface 

 marked by coarse and fine, undulating, lamellose lines of growth. Tube 

 ornamented with two or four lateral and two ventral revolving rows of semi- 

 tubular spines, formed by a retral arching of the lamellose lines of growth, 

 and having an elevation of from four to ten mm. Generally on the ventrum, 

 and occasionally on the sides, the margins of the laminae, which at intervals 

 are elevated into spines, are continued along the test, forming low, rounded, 

 revolving ridges, giving the tube a hexagonal form, rounded on the dorsal 

 side. On the ventral side these revolving ridges limit the sinus in the striae 

 of growth. Sinus deep, rounded, broad, having a width equal to one-fourth 

 the diameter of the tube. 



Internal mould essentially smooth, but preserving remains of the surface- 

 markings and the ornaments of the test, with the striae and furrows of the 

 crenulations. 



The largest fragment of this species observed, which is septate throughout, 

 has a diameter of 180 mm., measured across the volutions. 



This species is characterized by the regular rows of semi-tubular spines and 

 the undulating lines of growth. The curvature of the tube is much greater 

 than in C. Jason, and the ornamentation is more regular and marked than in 

 tli.it species. The internal mould of G. validum is very similar, but it has 

 shown no evidences of an ornamentation from expansions of the test or undu- 

 lations of the tube. The specimens of this species are found in considerable 



