320 Mr. Hogg on the Marine Production 



black specks situated on the front, which I concluded without 

 doubt to be its eyes. 



Tab. IX. Fig. 1. represents, in its natural size, the under 

 surface of a portion of this substance, broken through the middle 

 of a perfect specimen, at right angles to its edge ; and shows 

 plainly the arrangement of the shells, which are expressed by 

 the shaded parts of the drawing. 



Fig. 2. is a similar section, somewhat magnified, to exhibit 

 more clearly the forms of the cells, contained between the two 

 layers of conglutinated sand. , 



Fig. 3. represents one of the minute shells in its natural size. 



Fig. 4. is a back view of the same, highly magnified. 



Fig. 5. is a young shell of Nerita glaucina, seen also from the 

 back ; which is here introduced to be compared with the last 

 figure. And for the same reason. Fig. 6. shows the aperture 

 and umbilicus of the shell, Fig. 5., in order to prove the exact 

 resemblance which it bears to Fig. 7-, another small shell, re- 

 presented from the side of the aperture and umbilicus, and mag- 

 nified on the same scale as Fig. 4. 



Fig. 8. is the same as Fig. 7. in its natural size. 



The exact similitude of these small testaceous bodies to the 

 livid Nerite, induces me to believe that they are the young of 

 that species. 



This substance is sometimes found with a small hole in each 

 of the cells opening on the under surface (as at Fig. 1.) : this 

 hole is formed by the shell contained in the cell, which, when 

 suflSciently grown, forces its way through the under coating of 

 sand, and thus exchanges its former abode for the shore. 



If a part of this production, when perfectly dry, be immersed 

 in muriatic acid, it will slightly effervesce, and the calcareous 

 particles will be dissolved ; and others which are indissoluble, will 



be 



