^^^7-] DR. J E. GRAY ON CATILLUS. 999 



the cavity of the ovate Catilli ; while the compressed Limpets have 

 the base arched ; that is to say, the side of the shell that embraces 

 the cylindrical stem, or fits into the concavity in the roots of the 

 large i^M«, is produced to fit the form of the body to which it is 

 attached. The Limpets, when placed on a flat board, rock from end 

 to end. 



The small thin shell of the small species that lives in Calcutta 

 diHers from the others in having tb.e side of the cavity rather pro- 

 duced, like the Limpet above described. Thev are said to have been 

 obtained in the Botanic Gardens and in the ditches near the city • 

 bill It IS not stated if they live on stones, or if they live on the stems 

 oi the plants ; if the latter, that may explain the peculiarity of their 

 lonn. 



The following species probably belong to this or the followino- 

 genus ; but their opercula have not been observed or kept :— ° 



1. Navicella entrecastkauxii, Re'cluz, Rev. Zool. 1841 

 p. 380 ; Reeve, t. 8. f. 32. 



Hab. Australia, Point Entrecasteaux, King George's Harl)our. 



2. Navicella orientalis. Reeve, Icon. t. 8. f. '33. 

 Navicella ccerulescens. Reeve, Icon. t. 7. f. 29. 



Hab. India: Calcutta, in the Botanic Gardens (on plants?). 



3. Navicella extmia, Reeve, Icon. t. 6. f. 26. 

 Navicella reticulata, Reeve, Icon. t. h. f. 20. 

 Hab. Ceylon {F. Layard). 



Tribe III. Orthopomina. Operculum oblong, rather elonx/ate ; 

 horny (true) ojjerculum triangular, rather oblique as regards 

 the axis of the horny plate ; shelly plate half oblong, rather 

 narrowed above and rounded at the upper edge, with a very 

 slight fold diverging from the nucleus to the left upper mar- 

 gin ; the anterior cartilaginous flap large, broad (Figs. ■\a,Ab). 



Fig. 4 a. 



Fig. 4«. Outer surface. Kg. 4i. Inner surfaoi 



Orthopoma, n. a;. 

 Shell ? ^ 



This form is described from a single operculum which was found 

 separated from the shells iu the drawer of Navicella in Mr. Cuming's 

 collection. I have no doubt it belongs to some shell in the col- 

 lection, and most likely one named and figured by Mr. Reeve, 



Mr. Cuming, fortunately, in some instances attached an operculum 



