TECTURA. 245 



very convex, thin, and beautiful. They evidently would 

 never have assumed the shape of the variety. 



It is the Patella intorta of Pennant, P. minor ox 

 Wallace, P. cceruleata of Da Costa, P. ccerulea of Mon- 

 tagu (but not of Linne), and P. cornea of Michaud. 

 The very young is Montagu's P. bimaculata. Couch's 

 shell of the last name was apparently a simple Ascidian, 

 perhaps a species of Cynthia. 



H. pectinatum [Patella pectinata, Linne) was wrongly 

 admitted into British catalogues on the authoritv of 

 Laskey. Linne gives as its habitat the Mediterranean ; 

 Payraudeau, Corsica; and R. T. Lowe, Mogador and 

 Senegal. 



Genus III. TECTU'RA* [Tecture) Cuvier. PLY. f. 5. 



Body more or less depressed : mantle fringed at or near its 

 edge : tentacles variable in length : eyes prominent, wanting 

 in some species : gills forming a short plnme, which is free, 

 and contained in a cavity over the neck on the right-hand side 

 of the head ; it is extensile, and sometimes protruded beyond 

 the shell : foot of moderate thickness. 



Shell conical, usually depressed, furnished with striae which 

 radiate from the crown, having in its embryonic state a curved 

 or semispiral apex ; crown not prominent, but projecting hori- 

 zontally, and placed near the front margin : pallia! scar nearly 

 marginal. 



I do not see any reason for placing this genus in a 

 separate family from that which includes the last two 

 genera. The difference in the length of the branchial 

 apparatus, on which so much stress has been laid by 

 some conchologists, is comparatively unimportant. In 

 each of these three genera the gills compose a single 

 row or plume, which is elongated and attached through- 

 out in Patella, and less so in Helcion ; while in Tectura 



* A covering over. 



