THE MARSH CERITHIUM. 



325 



The color of the present species is slightly variable, but in the individual specimen the 

 shell is marked with bold, zigzag streaks of white and pale buff, and the interior is pure white 

 at the lip, changing to beautiful canary-yellow in the interior. The operculum is thick, hard, 

 solid, and highly burnished, as if overlaid with glass ; its edge is regularly and finely grooved. 



Several allied shells are inhabitants of the fresh instead of the salt waters, and are known 

 as Neritines. 



One of the most curious of these shells is the Spined Neritina. The animal of the 

 Neritina is not unlike that of the preceding genus, but there are one or two minute differences. 

 The operculum is shelly, with a flexible border, and has some small teeth on its straight edge. 

 All the Neritina? are globular in their general shape, darkly spotted or banded with black and 

 purple, and covered with a polished bone-like epidermis. The color of the Spined Neritina is 

 deep green-black on the exterior, and blackish-white within. The shell is thick and solid 

 at the aperture, but becomes thinner towards the interior. 



The Crown Neritina. The color of this shell is gray, diversified with dark streaks. 

 One species of this genus, the River Neritina {Neritina fiwoidtilis), is found in the rivers of 

 Northern Europe. 



The curious shell represented in the accompanying illustration is an example of another 

 family, that of the Clubs, or Cerithiada?. The shell of the Cerithites is spiral, more or less 

 elongated, and the operculum is horny and spiral. The tentacles are placed rather far apart, 

 and the eyes are set on very short footstalks. These creatures inhabit either marine, brackish, 

 or fresh water. 



The Pelican's Foot, sometimes called Spoit-siiell, on account of the manner in which 

 the aperture is lengthened into a kind of spout in front, has a rather elongated spire, and is 

 considerably tuberculated on the exterior. As the 

 animal approaches maturity, it adds fresh substance 

 to the lip, until it bears some resemblance to the 

 webbed foot of an aquatic bird. The animal has a 

 short and rather abrupt muzzle, and moderately long, 

 cylindrical tentacles, having the eyes set on protruber- 

 ances near their base. Only three species of this genus 

 seem to be at present known, but they have a wide 

 range of locality, being spread over the greater part of 

 the world, and found at various depths, sometimes 

 being taken in a hundred fathoms of water. 



The color of the Pelican's Foot is white, with a 

 tinge of pink, and white inside. The shell is thickly 

 and strongly made, and heavy in proportion to its 

 weight. As may be seen by reference to our engraving, 

 which is of natural size, it is not a large species, seldom 

 measuring more than two inches in length. 



The Great Club-shell is considered a species belonging to the typical genus of the 

 family. It is rather a large genus, containing at least one hundred known species, and 

 ranging over the whole world. The largest species are, as is usually the case, to be found 

 within the tropics. The shell is considerably elongated, and with many whorls, and the 

 " varices " or marks of growth are partially visible on the exterior. The aperture is decidedly 

 small when compared with the dimensions of the shell, and has a somewhat twisted canal in 

 front. The outer lip is rather wide, and the inner is much thickened. 



One of these shells, the Marsh Cerithiuji {CeritMum palustre), is supposed by some 

 persons to produce the strange sub-aquatic musical sounds that exist in several Eastern lakes. 

 A detailed account of these sounds, together with the reason for this conjecture, may be found 

 in Sir J. E. Tennent's "Natural History of Ceylon." 



The color of the Great Club-shell is deep chocolate-brown on the exterior, slightly mottled 

 with varying tints, and the interior is brown, but without the chocolate hue. 





-us;., 



PELICAN'S FOOT.— Aporrhais pes pelicani. 



