28: 



I 



Fio. 219. Connlaria undidaf(t. 



Distinguish- 

 ing Charac- 

 ters. — Qiiad- 

 rang-nlar basal 

 section ; shal- 

 low o•roO^•e in Fig SIQA Enlargement ot 

 o part of surface of Conidand 



flin ppTifpT i^i undulata, showing crenulate 

 Lilt; ecu LCI ui character of striae, x 6 (after 



each face: fine ^*^^'' 



transverse surface striae, slightly 

 deflected at the median groove, 

 and crossing the angles ; pustulose 

 or crennlate character of stria^; 

 smooth interstriate s}»aces, which 

 are about twice as wide as the 

 striae. In external molds the stria> 

 will be represented by narrow 

 grooves, in which the jinstulose or 

 crenulate character appears, sej)- 

 arated by wide flat ridges, which Natural size (after Haii,. 



represent the wider smooth interstriate spaces. 



A fragment of an external mold was found between four- 

 teen and twenty-three feet below the Encrinal limestone, at 

 Section 7. 



Class Cephalopoda, Cuviek. 



The cepbalopods are the most highly developed molluscs, possessing a 

 distinct, well-defined head, a circle of eight or more arms surrounding 

 the mouth and generally furnished with suckers or hooks, a funnel -like 

 " liyjwnome" or swimming organ, and a highly-developed nervous 

 sj'stem. The majority of modern genera are naked, or with only a rudi- 

 mentary internal shell (squids, cuttle-fish, etc.). Nautilus is the only 

 modern genus with a typical external shell. 



The shells of cephalopods are chambered, i. e., divided, by a series of 

 transverse floors or septa, into air chambers. The last or living chamber 

 lodges the animal. The septa are pierced by a corresponding series of 

 holes, wiiich are often prolonged backwards or forwards into siphonal 

 funnels, the whole constituting the siphnncle. The line of junction be- 

 tween the septum and the shell (the suture) is either simple or complex, 

 and is best shown when the shell has been removed, after the chambers 

 have been filled up by foreign material, a condition commonly realized 

 in fossil forms. 



