THE LADDER-SHELL. 



209 



SOLARIUM PERSPECT1VUM. 



Stylina has a glassy, globular shell, with a tapering apex and a sinistral nucleus. The animal 

 has a thick mantle, which is bent over the last whorls of the shell. It lives attached to the spines 

 of Sea Urchins, or buried in living Star-fishes and Corals. It is found 

 in Britain, the West Indies, Philippines, and the Galapagos. 



FAMILY XL SOLAKIAD^. 



The proboscis in tliis family is 

 retractile, and the tongue (according 

 to the observations of Dr. Gray) is 

 entirely unarmed ; the tentacles are 

 laterally folded, the eyes are on the 

 upper surface at their bases; the mantle 

 is included ; foot moderate, and formed 



for walking ; the operculum horny, spiral, oval, or circular. The genus Solarium, or the " Staircase 

 Shell " so named because the spiral edges of the whorls seen in the umbilicus have been fancifully 

 compared to a winding staircase has a depressed orbicular shell, with a wide and deep umbilicus. The 

 aperture of the shell is squarish, the peristome is thin, the operculum horny and sub-spiral. There 

 are twenty-five species, all from sub-tropical and tropical seas, and very widely distributed. 



FAMILY XII. SCALARIAD^E. 



The animals in this family are predaceous. The mantle is enclosed with a rudimentary siphoual 

 fold ; the foot is obtusely triangular and grooved below ; the tentacles are slender, and the eyes are 

 placed at their outer bases ; the operculum is horny and spiral. The shells are nearly all white ; they 

 are spiral and turreted, and are ornamented with varices ; the aperture is circular, without any 

 notch or canal. The shells are remarkable for their extreme elegance of form. 



The genus Scalaria, known commonly as the " Wentletrap," or " Ladder-shell," has mostly 

 a pure white lustrous shell, the whorls of the turret-like shell being round and 

 nearly separate, merely united by the sharp transverse ribs. When molested, 

 the animal exudes a purple fluid. The species exceed one hundred in number, 

 and range from low water to one hundred fathoms. Most of the species are tropical, 

 but there are exceptional species found on the coasts of Greenland and Norway. 

 The others are almost woi-ld-wide. In the "Wentletrap" (Scalaria pretiosa) the 

 periodic mouths encircle the shell- whorls, which are sometimes separate, and con^ 

 tribute not a little to the beauty of this once costly conchological treasure. 



SCALAKIA 

 PRETIOSA. 



FAMILY XIII. CERITHIAD.E. 



In this family the shell is spiral and many-whorled, the mouth 

 of the shell is channelled in front, and the outer lip is usually 

 expanded in the adult shell. The animal has a broad and short rostrum, with 

 the tentacles wide apart ; the eyes are on short stalks united to the base of the 

 tentacles. The mantle-margin has a rudimentary siphon-fold in front ; the foot is broad 

 and short, and angular in front : the operculum horny and spiral. The members of 

 this family are met with in marine, estuarine, and fresh-water localities. 



The genus Cerithium, or the " Horn-shell," has a turreted, many-whorled shell, 

 with indistinct varices ; the canal is produced in front, and slightly recurved ; the 

 columella is thickened and callous behind. Cerithia are found in all parts of the world. 

 More than one hundred living species have been described. 



Potamides* is the name given to a group of fresh-water Cerithia, with thick olive- 

 brown epidermis, and an orbicular many-whorled operculum. They are found chiefly 

 World, especially in Africa and India, inhabiting the mud of large rivers. 



The genus Aporrhais, or the "Spout-shell," is a shell with an elongated spire, 



CERITHIUM 

 ALUCO. 



in the Old 

 composed of 



From potamos, a river ; and cidos, used in the sense of species. 



217 



