764 



DIVISIONS OF THE GASTROPODA. 



been found in the Carboniferous Limestone, but most of the fossil 

 forms are Cretaceous and Tertiary. 



Family 3. Capulid^e {=Calyptr(zid(z). — In this family the shell 

 is conical and patelliform, with a more or less spiral apex, the interior 

 being simple, or divided by a shelly process to which the adductor 

 muscle is attached. The margin of the shell-aperture is thin and 

 entire, often more or less modified in outline by the habit which the 

 animal possesses of fixing itself, with the aperture closely fitted, to 

 some foreign body, such as a Crinoid. 



The genus Calyptrcea, in the wide sense in which it has gener- 

 ally been defined, includes the so-called " Cup-and-saucer Limpets," 

 in which the interior has a half-cup-shaped process attached to the 

 apex of the shell, and open in front. The earliest forms of this 

 type appear in the Cretaceous rocks, and the genus still survives. 

 In the genus Crepidula (fig. 645, e) there is a shelly partition cover- 

 ing the posterior half of the interior of the shell. The fossil forms 

 of this genus date from the Cretaceous period. Hipponyx, again, 

 comprises thick and obliquely conical shells, with a posterior apex, 

 and often provided with a shelly basis marked by a distinct horse- 

 shoe-shaped muscular impression (fig. 645, d). The genus ranges 

 from the Cretaceous rocks to the present day. 



By far the most important genus of this family, palaeontologically 

 speaking, is Capulus (Pileopsis) itself, including the so-called " Bon- 

 net-limpets " of the present day. The Palaeozoic shells which have 

 been included under the name of Platyceras (=Acrocu/ia) appear to 

 be identical with Capu/us, or, at any rate, to be distinguished from 



this by characters of no more 

 than sub-generic value. In the 

 genus Capulus, employing this 

 name in the general sense in- 

 dicated above, the shell is con- 

 ical, with a posterior sub-spiral 

 apex, and, generally, a horse- 

 shoe - shaped muscular impres- 

 sion. The aperture is greatly 

 enlarged, and its margins are 

 essentially entire ; but owing to 

 the fact that the shell is usually 

 affixed for lengthened periods to 

 foreign bodies, the lips may be- 

 come more or less sinuated or undulated (figs. 646, 647). The 

 shells of this genus may, as a rule, be recognised by their obliquely- 

 spiral or straight, conical shape, their wide aperture, and the 

 absence of a columella. They may be dextral or sinistral, and 

 the surface may be simply marked with concentric lines of growth, 



Fig. 646. — Capulus {Platyceras) ventricosus. 

 Silurian. (After Hall.) 



