GASTEROPODA. 247 



the Cretaceous and Tertiary Rocks; but they attain their 

 maximum in existing seas. 



The Scorpion-shells form the genus Pteroceras (fig. 207), in 

 which the shell of the adult has its outer lip furnished with 

 long claws, one of which forms a posterior canal close to the 

 spire. Many fossil species are known, commencing in the 

 Lias. 



In the genus Rostellaria, the spire is long, and has the 

 posterior canal running up it. Many fossil species are known, 

 commencing in the Cretaceous Rocks. The outer lip is 

 always expanded, and in some forms is enormously so. 

 Lastly, the genus Seraphs comprises smooth shells, with a 

 short or obsolete spire, a thin outer lip, and a long narrow 

 mouth. The fossil species date from the Eocene Tertiary. 



FAM. 2. MURICID^E. Shell with a straight anterior canal, 

 the aperture entire posteriorly. Foot broad. The MuricidcB 

 are essentially characteristic of the Tertiary and Recent 

 periods. They commence, however, in the Jurassic Rocks, in 

 some doubtful examples, and they are certainly represented 

 in the Cretaceous Rocks by not a few forms. 



In the genus Murex the canal is often very long, and may 

 be partially closed ; the shell is ornamented with longitudinal 

 ridges or rows of spines (varices), and the aperture is rounded. 



In the nearly-related Typhis (fig. 208) there are tubular 

 spines between the varices, and the last of these lodges the 

 posterior siphon. Both 

 Mnrex and Typhis com- 

 mence in the Eocene Ter- 

 tiary, and have attained 

 their maximum in existing 

 seas. 



Pisania commences to 

 be represented in the 

 Eocene, as do the genera 

 Ranella, Triton, and Can- 

 cellaria. Fasdolaria and 

 Pyrula commence their 



existence in the Cre- F ' g ' 2 8 - / >'^ *<^ ^enele-ary. 



taceous Rocks ; and Turbinella and Trichotropis do not make 

 their appearance till the Miocene. Lastly, the great genus 

 Fusus, distinguished by the spindle-shaped, many-whorled 

 shell, and long straight canal (fig. 209), appears to have its 

 commencement in the Oolites. Fusi become very numerous 

 towards the close of the Cretaceous period, and they are 

 very plentiful in the Tertiaries. One of the common fossils 



