1867-] 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 Fuci, 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 

 differs from the others in having the side of the cavity rather pro- 

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

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

 but it is not stated if they live on stones, or if they live on the stems 

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

 form. 



The following species probably belong to this or the following 

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



1. Navicella entrecasteauxii, Recluz, Rev. Zool. 1841, 

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



Hab. Australia, Point Entrecasteaux, King George's Harbour. 



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 eximia. Reeve, Icon. t. G. f. 2fi. 



Navicella reticulata, Reeve, Icon. t. .5. f. 20. 

 Hab. Ceylon (F. Layard). 



Tribe III. Orthopomina. Operculum oblong, rather elongate ; 

 horny (true) operculum triangular, rather oblique as regards 

 the axis of the horny lilate ; 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. 4a, Ab). 



Fig. 4 a. Fig. 4 b. 



Fig. A a. Outer surface. Fig. 4i. Inner surface. 



Orthopoma, n. g. 



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 



