CEPHALOPODA. 379 



Chamber of habitation slightly contracting toward the aperture, having a 

 length two-thirds greater than the ventro-dorsal diameter of the tube at the 

 last septum. The crenulations are shown on the internal mould as low, 

 rounded ridges and striae. Aperture expanded, slightly oblique, opening a 

 little outward. 



Air-chambers regular, gradually increasing in depth toward the grand 

 chamber, varying from six to nine mm. in the length of 150 mm., measured 

 on the convex side of the outer volution. There are about two air-chambers 

 between two of the transverse ornaments of the test. Septa smooth, with a 

 concavity equal to the depth of the air-chambers. Sutures straight and at 

 right angles to the spiral axis of the tube. 



Siphuncle close to the ventral side. Its elements have not been observed 

 in the cavities of the air-chambers. 



The test has a thickness of .5 mm. Surface marked by fine, irregular, 

 lamellose lines of growth, curving in a retral direction over the ventro-lateral 

 faces. On the ventro-lateral angles the lamellose expansions of growth are 

 suddenly bent backward at each alternate septum, and raised into semi-tubu- 

 lar nodes or spines. These processes incline toward the aperture, and are 

 continued as lamellose expansions of the test over the dorsal and lateral faces 

 of the tube, reaching an elevation of ten mm., and extending to the ventral 

 side of the inner adjacent volution. Sinus broad, rounded, deep. 



The internal mould preserves the striae and furrows of the crenulations, 

 and shows transverse, elongate nodes, corresponding to the tubular processes 

 of the test, 



The largest specimen observed has a diameter of 120 mm., measured 

 across the disc, and the tube has a diameter of thirty mm. at the aperture. 

 The majority of the specimens have a diameter across the disc of from 110 

 to 1 16 mm. 



This species is more closely coiled, and has a greater number of volutions 

 than any of the preceding forms. It resembles G. pautinodum, and may be dis- 

 tinguished by its slightly more open spiral, broader and less triangular section, 

 and its more frequent and numerous spines on the ventro-lateral angles. These 



