CEPHALOPODA. 4fil 



ceding. The depth of the chambers is sometimes five mm. where the 

 diameter of the tube is thirty-five mm., and from three to four mm. when 

 the tube has a diameter of nineteen mm. 



The septa are thin, presenting, at their origin on the umbilical side, a 

 gentle forward curve for the distance of a few millimetres, and are a little 

 more abruptly recurved to about the same depth. From this point they 

 make an abrupt angular return describing a broad curve over the middle of 

 the lateral face, and descending a little deeper than before, they make an 

 acute return and describe a shorter curve to the peripheral margin. By this 

 disposition of the septa we have a narrow convex umbilical saddle, a broad 

 central or lateral saddle, and a narrower peripheral saddle of a little greater 

 witlth, but more convex than that on the umbilical side. It gives a short 

 acute lobe, with its apex about one-fourth the width of the tube from the 

 umbilical side, and a larger triangular lobe, with its apex at a point about 

 one-fourth the width of the tube from the peripheral margin. The direc- 

 tion of the septa on the periphery is undetermined. The sutures are usually 

 but faintly impressed, and often very obscure upon the casts of the shell. 

 Siphuncle unknown. 



Test strong, rarely preserved, having in old shells an approximate thick- 

 ness of nearly two mm. on the chamber of habitation. Surface marked by 

 strong sublamellose striae, which make a gentle retral curve over the lateral 

 face of the volution, and arching somewhat abruptly forward as they approach 

 the margin of the periphery are suddenly recurved over the ventral side. 

 The striae are somewhat regular and even on the lateral faces of the volutions, 

 there being often about six in the space of five mm., and on the smaller 

 volutions ten in the same space ; approaching the aperture they become 

 stronger, and there are only three in the space of five mm. The sinus, 

 inferring from the direction of the striae, is abrupt and of moderate depth. 



The internal mould is essentially smooth, and but faintly marked by the 

 suture lines. The external striae are sometimes impressed upon the cast, and 

 in some conditions, the partial casts or interior of the shell, show a punctate- 

 marking. 



