6 



RANDOM NOTES ON NATURAL HISTORY. 



The Shell - Bearing Mollusca of Rhode 

 Island. 



[BY HORACE F. CARPENTER.] 



Chapter II. 

 CuviER named the second grand type of 

 animal creation Mollusca, from the Latin, i 

 mollis or soft, meaning soft-bodied animals. | 

 This term is not exchisively characteristic j 

 of this department of nature. There are | 

 many soft-bodied animals not included in , 

 the Mollusca, and there are also members j 

 of this group which are not wholly soft. i 



Mr. Edward 8. Morse, of Salem, Mass., | 

 in a paper read before the Essex Institute, j 

 called " A Classification of Mollusca, based 

 on the principle of Cephalization,'" proposed 

 the name " Saccata," suggested by Alpheus 

 Hyatt, as better expressing their plan of 

 structure : the stomaclis and viscera of all 

 mollusks being enclosed in a fleshy sac, 

 which, in the different classes, is open or 

 closed at one or both ends ; but as natural- 

 ists have not seen fit to adopt this change 

 of nomenclature, we must continue at pres- 

 ent to use that given by Cuvier. Linnseus 

 was the first to systematize the study of 

 animals and plants, and gave to each variety 

 two Latin names, the generic and specific, 

 viz.: Mytillus edulis, the edible mussel. 

 Afterwards Cuvier established the system 

 of the division of animal forms into types, 

 classes, orders, and families. 



The study of the anivials of the type 

 Mollusca, is called Malacology. Conchology 

 is the study of the shells (secreted by the 

 animals, forming the houses in which they 

 live), together with descriptions of the 

 habits, location, distribution, etc. In pre- 

 parino- these papers on the " Conchology 

 of Rhode Island," I shall recognize only 

 those mollusks which secrete a calcareous 

 shell. , ,^ , 



The Mollusca proper, excluding the Mol- 

 luscoida (Brachiopoda, Tunicata, and Bryo- 

 zoa) , may be divided into two great groups, 

 as follows : 



1. Encephala. The animal possesses a 

 head, and is usually, but not always, pro- 

 tected by a spiral, or otherwise univalve 

 shell. Example, the snail. 



2. Acephala. The animal has no head, 

 and is always protected by a bivalve shell, or 

 one consistiiig of two parts, connected at 

 the back by a ligament, or hinge. Example, 

 the oyster. 



The Encephala comprises four out of the 

 five classes into which the Mollusca are 

 divided, and includes more than three-fourths 

 of the whole number of known molluscous 

 animals. These classes are : 



1. Cephalopoda. These animals live in 

 the ocean, and are fouud in all parts of the 

 world. They are carnivorous in their hab- 

 its. They have large heads, separate from 

 the body portion ; the name of the class is 

 given to it from the mouth of the animal 

 being surrounded by eight or ten long fleshy 

 arms, or feet, and arising from the top of 

 the head. 



2. rteropoda. These animals also inhabit 

 the ocean, swimming by means of a pair of 

 wings extending laterally from the back of 

 the head. 



3. Gasteropoda. The under side of the 

 body forms a muscular foot, by which they 

 crawl along, dragging the shell after them, 

 to which they are attached by the mantle. 



4. Scaphopoda. The shell is a hollow 

 cylinder, open at both ends; the animal 

 with a rudimentary head ; foot vermiform, 

 furnished with lobes. 



5. Acephala. This term is synonymous 

 with Pelecypoda, Lamellibranchiata, and 

 Conchifera," the meaning of which will bo 

 explained in its proper place. 



Class 1. Cephalopoda. 

 This first and highest class of the Mol- 

 lusca is divided into two orders : 



1. Dibranchiata. Breathing by a single 

 pair of branchia; or gills. Mandibles, horny. 

 Arms, eight or ten, furnished with rows of 

 suckers. Shell, internal or none. 



2. Tetrabranchiata. Breathing by two pair 

 of branchiie. Mandibles, shelly. Arms, 

 very numerous, without suckers. Shell, ex- 

 ternal, chambered; capable of containing 

 the animal. 



Order 1. Dibranchiata. 



Sub Order 1. Octopoda. Arms, eight, 

 sessile ; no shell. 



Sub Order 2. Decapoda. Arms ten, eight 

 of which are sessile, and two (longer) ten- 

 tacular. Shell internal. 



Sub Order 1, Octopoda, consists of three 

 families, containing thirteen genera, and 

 eighty-three described species, none of which 

 having shells, are all excluded from these 

 papers on " the Shell-bearing Mollusca of 

 Rhode Island." 



Sub Order 2, Decapoda, consists of eleven 



