10 BRITISH CRETACEOUS BRACHIOPODA. 



shape of the muscular impressions visible in the interior of both valves, so well described 

 by that conscientious observer, M. Bouchard, who has devoted much time to the study of 

 this genus. 1 He states, that "The Cranias present two kinds of impressions left by the 

 adductor muscles, — those which are often deeply excavated in the thickness of the valves 

 are produced by muscles that do not deposit calcareous matter, and which, by their 

 insertion on the valve, prevent the mantle from depositing its calcareous substance on 

 the part occupied by their base; we then see this pallial secretion surround the base of the 

 muscles, and circumscribing these impressions with a calcareous crest or rim. The 

 others, on the contrary, possessing the faculty of depositing calcareous matter, form 

 projections that assume all kinds of shapes ; therefore, in the interior of the upper 

 valves of Crania Parisiensis and C. abnormis, we perceive the muscular deposits under the 

 form of lanceolate and pedicular laminae, rising with age from the bottom of the valve, to 

 the height of several millimetres." The upper valve, from its extreme thinness, is 

 seldom preserved, while the attached valve is very abundant. In England, it is sometimes 

 found in the Chalk of Kent and Sussex, but it cannot be said to be common. In Plate I, 

 I have endeavoured to illustrate a few of the principal variations assumed by this shell 

 from a beautiful series of specimens, for which I am indebted to the kindness of several 

 friends. 



Plate I, fig. 1 . A specimen, enlarged, of the attached valve, very adult, from Gravesend, 

 in the collection of Mr. Bowerbank. 

 ,, fig. 2 a . A very adult specimen, enlarged, from the same locality, in the collec- 

 tion of Mr. Bowerbank. 2 

 „ fig. 2 6 . A very adult specimen of the upper valve, likewise from the above- 

 mentioned collection. 

 „ fig. 3. A fragment, much enlarged, of the lower valve. 

 ,, fig. 4. Profile view of the upper valve. 

 „ fig. 5. Profile view of the lower valve. 



,, fig. 6. The exterior of the upper valve, from the collection of Mr. Bowerbank. 

 ,, fig. 6". Profile view of both valves, united, from the same collection. 

 ,, fig- 7. A remarkably fine specimen, from the chalk of Meudon, in my collec- 

 tion, placed here to show how the shells sometimes clustered near 

 each other in the young state ; not finding room as they grew to 

 develope themselves, they assumed the shape the space admitted, 

 indenting and projecting one above another, one of the specimens 

 preserving still its upper valve. 



1 'Memoire sur un Nouveau Genre de Brachiopode,' (' Annales des Sciences Nat.,' vol. xii, p. 84, 1849.) 



2 This valve has been rarely figured. Mr. Dixon gives a correct illustration in his work, and in a plate, 

 entitled ' Collection de M. H. Michelin,' published some years back. Figs. 2 and 3 illustrate this valve, 

 from Meudon, where it is extremely rare. 



