490 FOSSIL INVERTEBRATED ANIMALS. 



the cerithium yigas. This is a very long and turriculated 

 shell, composed of from thirty to thirty-five whorls. The 

 aperture is oblong and a little oblique, terminated at the base 

 by a canal, whose extremity is somewhat recurved. It is some- 

 times from fifteen to sixteen inches or more in length, on a 

 diameter of four or five inches at the last whorl. A thread, 

 turned over its suture from the summit to the base, was found 

 to be more than eight feet in length. In proportion as the 

 animal grows, it abandons the summit of the shell for the 

 aperture. It forms concave septae as it retires. This shell, 

 being extremely heavy, and at the same time very much pointed 

 at its summit, is exposed to be broken in that part during the 

 life of the animal. The attrition which some of them have 

 experienced in being transported from one place to another, 

 has so much shortened and worn them on one side, that the 

 columella of the first whorls becomes visible. If the animal 

 had not retired, and in retiring had not formed septae, it would 

 have been exposed to be mutilated or attacked in this part by 

 its enemies. Nature, to prevent this, bestowed upon it the 

 faculty of withdrawing and forming septae. The same phe- 

 nomenon is observable in all univalve shells, and more particu- 

 larly in those which are turriculated. This species is remark- 

 able, not only for its giant size in the abstract, but also for 

 the sudden advance of that size beyond the other species of its 

 genus. It is found in all the strata of shelly limestone. They 

 are so common in the falunieres of Hauteville, that, in some 

 places in the neighbourhood, they use them in making the 

 high roads. This shell is also found in the existing state in the 

 South Seas. There are in the Placentine territory, and many 

 other localities, an immense number of cerithian shells in the 

 fossil state. We are indebted to Mr. Sowerby's valuable work 

 on Mineral Conchology for most of our figures of fossil shells, 

 to which we have added a few from our own cabinet. 



The remains of impressions of Crustacea found in the 

 bowels of the earth have been designated under a variety of 



