CEPHALOPODA. 345 



which is shallower than the preceding. The preceding four or five chambers 

 have a depth of five min. each : beyond these the tube contracts very rap- 

 idly to the apex, and their depth has not been observed. In the shorter 

 and more globose individuals the chambers have a depth of three mm., and 

 the tube contracts abruptly from the second or third chamber posterior to 

 the chamber of habitation. Septa thin and smooth, so far as observed ; 

 moderately concave. Sutures straight and horizontal. 



Siphuncle near the ventral side, with a diameter of two mm at the last 

 septum. 



Test strong, having a thickness of 1.6 mm. over the chamber of habitation. 

 Surface marked by fine, irregular, lamellose lines of growth. The surface 

 and structure of the inner or nacreous layer is characterized by indistinct 

 lines of growth, crossed by fine, longitudinal strise. At nearly regular inter- 

 vals of six to nine striae, one of the lines is larger and stronger than the 

 intermediate stria), giving the tube a furrowed appearance. The sinus in the 

 lines of growth over the ventral side corresponds in size and position to 

 the small aperture, but is not quite so abrupt. 



Internal mould smooth, with the suture-lines well marked. 



The largest individual observed has a length of fifty r -eight mm., of which 

 twenty-five mm. pertain to the chamber of habitation, at the base of which 

 it has its greatest transverse diameter of forty mm. Five air-chambers are 

 shown before the truncation of the tube commences, which has obscured the 

 preceding chambers. Many of the specimens, having a transverse diameter 

 nearly as large as in the preceding, contract very rapidly from a point imme- 

 diately at the base of the grand chamber, giving them a gibbous or sub- 

 globose form. 



This species is distinguished by its ovoid form and the characters of the aper- 

 ture. It somewhat resembles G. pingue and G. raphanus. It differs from G. 

 ■i/e in the more rapidly expanded septate portion, and the position of the 

 plane of greatest transverse section. G. raphanus has a more slender tube, and 

 U less gibbous on the chamber of habitation. 



This form is especially interesting as furnishing the only positive evidence of 

 44 



