285 



Fig. 219. Conularia undulata. 



Distinguish- 

 ing Charac- 

 ters. — Quad- 

 rangular basal 



section ; shal- 

 low groove in F I G -„ 219 -S Enlargement of 



" part of surface of Conularia 



tliA ppntpr nf undulata, showing crenulate 

 Liie ceil lci ui cnaracter of strise< x 6 (att ,. r 



each face; fine Hall) " 

 transverse surface striae, slightly 

 deflected at the median groove, 

 and crossing the angles ; pnstnlose 

 or crenulate character of stria?; 

 smooth interstriate spaces, which 

 are about twice as wide as the 

 stria?. In external molds the striae 

 will be represented by narrow 

 grooves, in which the pustnlose or 

 crenulate character appears, sep- 

 arated by Wide flat ridges, which Natural size (after Hall,. 



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. Cuvier. 



The cephalopods are the most highly developed molluscs, possessing si 

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

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

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

 system. 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, which are often prolonged backwards or forwards into siplwnal 

 funnels, the whole constituting the siphuncle. 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. 



