3340 



THE MOLLUSKS OR SHELLFISH 



Rhachiglossa, Taenioglossa, Ptenoglossa, and Gymnoglossa. A large proportion 

 of the Pectinibranchs are furnished with a long proboscis, extensile and retract- 

 ile at the will of the animal. In almost every instance, mollusks of this proboscis- 

 bearing group are provided with shells which may be recognized by a notch or 

 canal at the front of the aperture, through which the so-called siphon is protruded. 

 This consists of a more or less elongate fold of the mantle, and conveys the water 

 to the branchiae. In another large section of the Pectinibranchs Rostrifera 

 there is no extensile proboscis, but the head terminates in a more or less prolonged 

 snout which is not retractile, and is termed the rostrum. These two groups, how- 

 ever, are now abandoned on the ground that better characteristics are furnished by 

 the radula. 



SECTION TOXOGLOSSA 



In this group, including the families Conidtz, Terebridce, Pleurotomidce , and Can- 

 cellariidce, the radula is composed of two rows of long, barbed, marginal teeth. The 

 cones {Conidce} form an extensive family, containing about five hundred and fifty 

 species. They have always been great favorites with collectors, on account of the 

 great beauty and variety of the color markings, and are almost exclusively tropical, 

 only a few species ranging northward to the Mediterranean and Japan. Some of 

 them have a very wide distribution, being found in the .Red Sea, Indian Ocean, and 

 in various parts of the Pacific. Others, on the contrary, have an equally limited 

 range. These animals are all predaceous, having a short strong foot, truncate or 

 square in front, and pierced with a water-bearing pore at the anterior part. The 

 head has two slender tentacles, with the eyes on the outside near the middle. The 

 siphon is long, and protruded through the notch at the anterior or narrow end of 

 the shell. They are not very active creatures, but crawl about slowly in holes in 

 the rocks, or fissures of coral reefs, in depths ranging from low-water mark to 

 thirty or forty fathoms. The shells are generally strong and solid, and as the 

 animal grows and requires more room, it absorbs the early whorls, leaving only a 

 very thin partition between them; but, in order to preserve the proper weight of the 



__ .__ shell, it thickens up the spire 



within. All the species are 

 formed on one plan, but the 

 extremes vary considerably in 

 form. This variation, differ- 

 ence of sculpture, periostra- 

 cum, and color, constitute the 

 characteristics upon which the 

 species are founded. Some 

 of the handsome and rarer 

 forms fetch very high prices. 

 Conus cedonulli, which is found 



TEXTILE CONE, Conus textile. in the West Indies, is, besides 



(Natural size.) being rare, remarkable for the 



