24 



from Patella without a knowledge of the soft parts of each individual 

 species. The fissure mainly answers the purpose of a vent ; but it is stated 

 by some writers to aid also in the conveyance of water to the branchial 

 cavity. 



The genera are — 



PlSSURELLA. PaRMOPHORUS. ACMiEA. 



Emarginula. Siphonaria. Gadinia. 



Genus 1. FISSURELLA, Bruguiere. 



Animal ; with a short muzzle terminating a tumid head, bearing 

 two subulate tentacles, at the external bases of which are the 

 eyes placed on rudimentary pedicles ; a range of numerous cirrhi 

 around the sides at the base of the very large foot ; mantle pro- 

 duced i?i front, with a fringe of cirrhi above its margin; anal 

 siphon in the form of a short, truncated, membranous canal, 

 projecting from the apical aperture of the shell : branchial 

 plumes two. 



Shell ; depressly conical, ovate or oblong-ovate, shield-shaped, ge- 

 nerally attenuated anteriorly, radiately striated or ribbed, per- 

 forated at the summit ; orifice oblong or nearly orbicular, some- 

 times contracted, sometimes excavated at the sides, most fre- 

 quently inclined anteriorly. 



The Fissurella, or Key-Hole Limpets, form a very attractive group for 

 the conchologist. Their shells are for the most part large and gaily painted, 

 and in the smaller species the deficiency of painting is often compensated 

 by an elaborate lattice of sculpture. The orifice at the summit of the 

 shell, which inclines more or less towards the front, and has a fold pass- 

 ing out of it in connection with the vent of the animal, varies materi- 

 ally in form in different species, but is always the same in the different 

 individuals of a species. It is mostly oblong, sometimes a little excavated 

 at the sides, but more frequently contracted in the middle in such a man- 

 ner as to give a somewhat toothed character to the margin. 



On reference to our figures in Plate I. of F. maxima and megatrema, it 

 will be seen that the comparative size between the animal and its shell is 

 variable in the extreme. The shell in most cases forms a complete cover- 

 ing to the animal, and while the disk is furnished with warts and papillse, 

 the mantle is more or less elaborately fringed at the edge. Whereas in 

 M. D'Orbigny's subgenus Fissurellidea, the soft parts are immensely en- 



