Introduction to Animal Morphology. 307 



facets, a posterior flat pyramid with an limbo, and a pair of 

 lateral areas ; each of these consists of a tegmentum under the 

 epidermis ; free between the mantle edge, and an articulamen- 

 tum, deeper layer ; there are two pair of joints, arficuli anfict and 

 postici, along the edge of the lateral areas. There is but one 

 family. 



II. Cyclobranchiata( Docoglossa) Limpets, with coni- 

 cal, inoperculate shells ; tentacles two, with eyes at their bases ; 

 foot large and flat ; radula with no middle plate, and ridged 

 lateral and intermediate plates. This includes the family 

 Pateilidae, with a long radula; teeth 2. 4. 2 ; muscular im- 

 pression on shell crescentic. The gills surround the head 

 (Patella), or may be interrupted there (Nacella). Lepetidse 

 have no eyes nor gills. Tecturidae have a free gill on the 

 right side of the neck. 



III. Aspidobranchiata herbivorous, rhipidoglossal ; 

 shell conical, spiral, flat or cap-like; foot large ; gills double; 

 penis none. This includes i. Fissurellidae foot large; 

 shells flat (Parmophorus) or limpet-like, with an apical (Fis- 

 surella) or pre-apical (Rimula) opening, or an anterior mar- 

 ginal fissure (Emarginula).* 2. Haliotidae shells ear-like, 

 nacreous within, left border with a row of holes along the 

 suture; an anal siphon. 3. Pleurotomaridae conical, fossil 

 shells, with a notched mouth, represented now by Anatomus 

 and Stomatia. 4. Trochidae scutibranchiate ; foot lobatc 

 and filamented along the side ; shell nacreous within ; oper- 

 culum smooth and calcareous in Phasianella ; orbicular, horny 

 in Turbo, with a solid convex, calcareous, inner pagina, 

 and a turbinate ventricose shell. Imperator has an oblong 

 or ovate operculum, also calcareous within ; in Adcorbis it is 

 calcareous, multispiral. Rotella has a flat, polished shell; 

 ihinula a horny concentric opcrculum and a turbinatcd 

 slu 11 : Trochus a membranous operculum and a conical shell 

 with a flat base. Gena is car-shaped, inoperculate, and Bro- 

 deripi.'i is limpet- like. 5. Ncriticlae scutibranchiate ; foot 

 oblong, triangular, not fringed ; shell thick ; pcritreme cres- 

 centic, spire not prominent ; opcrculum calcareous, pauci- 

 spirul, often articulate. Ncrila is marine ; Neritina freshwater ; 



This genus has a rudinn ;;!i^crous 1- 



