WOODWARD HIPPURITID^. 



41 



intelligible if stated alone, and not of sufficient importance to form 

 the subject of a communication to the Society ; and it is only upon 

 the express invitation of the President that I have ventured to offer 

 a general summary of a matter so often discussed. 



Description of the Shell of the Hippurites. — Hippurites are bivalve 

 shells, which were attached to the sea-bed, and usually gregarious, 

 Hke Oysters ; often adhering together by their sides, or growing one 

 upon the other. They are conical when young ; but soon become 

 cylindrical, as they lengthen upwards without increasing in diameter. 

 Some are straight, others curved ; one of the most common, H. cornu- 

 vaccinnm, is shaped like a cow's horn, and attains the length of a 

 foot or more. 



On one side there are three longitudinal furrows, extending from 

 the base to the summit ; the upper valve is nearly flat, and is per- 

 forated by numerous pores ; sometimes there are two eye-like depres- 

 sions, as in H. bi-oculatus. 



When broken with a hammer, the shell is found to consist of two 

 layers ; the outermost is readily detached, leaving a core, which is 

 furrowed lengthwise. The outer layer is compact and dark-coloured ; 

 its solidity is caused by the infiltration of carbonate of lime. Spe- 

 cimens, however, from the Chalk of Angouleme are quite porous and 

 brittle. Here the outer shell consists of a succession of corrugated 

 layers ; the wrinkles radiate from the inner margin and subdivide 

 and anastomose repeatedly, leaving interstitial pores. By the appo- 

 sition of these pores in the successive layers, long unequal tubes are 

 formed parallel with the long axis of the shell, and opening on its 

 rim. 



The inner layer is white and laminated, like the interior of an 

 oyster-shell, with spaces between the laminae, like those of the 

 Water-Spondylus, and which are of frequent occurrence in the Oyster 



Fig.* 1. — Section of a fragment o/Ostrea cornucopise, showing the 

 spaces formed by the lamince in the interior of the shell. 



also. The laminae are as thin as writing-paper, sometimes vesicular. 



* I am indebted to Dr. J. E. Gray, of the British Museum, for the use of the 

 woodcuts, which have been prepared for the * Museum Catalogue.' 



