vin PHYLUM MOLLUSCOIDA 359 



2. DISTINCTIVE CHARACTERS AND CLASSIFICATION. 



The Brachiopoda are Molluscoida in which the body is enclosed 

 in a shell formed of two parts or valves which are respectively 

 dorsal and ventral in position. The body occupies only a small 

 portion of the space enclosed by the shell, and is usually attached 

 to foreign objects by a posteriorly placed stalk or peduncle : it 

 gives off dorsal and ventral reduplications, the mantle-lobes, which 

 line the valves of the shell and enclose a large mantle-cavity. 

 From the anterior surface of the body is given off a lophophore 

 which surrounds the mouth, and is beset with ciliated tentacles. 

 There is a ridge-like pre-oral lip which is continued on to the 

 lophophore. The enteric canal is usually V-shaped, and is 

 divisible into gullet, stomach, and intestine : there is a pair of 

 digestive glands. The ccelome is spacious, and is continued into 

 the mantle-lobes. A heart is usually present, attached to the 

 stomach. The excretory organs are one or two pairs of nephridia 

 which act also as gonoducts. The nervous system is a ganglionated 

 circum-ossophageal ring : sense-organs are usually absent in the 

 adult. The sexes are separate or united. Development is accom- 

 panied by a metamorphosis. 



The class is divided into two orders : 



ORDER 1. INARTICULATA. 



Brachiopoda in which the shell is mainly composed of chitinoid 

 material with a varying proportion of calcined substance : the 

 valves are not united by a hinge, and there is no shelly loop for the 

 support of the lophophore. An anus is present. 



Including Lingula, Crania, Discina, &c. 



ORDER 2. ARTICULATA. 



Brachiopoda in which the shell is formed of oblique prisms or 

 spicules of calcium carbonate : the two valves unite by a definite 

 hinge, and there is usually a shelly loop, for the support of the 

 lophophore, developed in connection with the dorsal valve. The 

 intestine ends blindly. 



Including Magellania, Terebratula, Rhynchonella, Cistella 

 (Argiope), &c. 



Systematic position of the Example. 



The genus Magellania, of which there are several species, 

 belongs to the family Terebratulidse, and to the order Articulata. 



The dissimilar valves of the shell articulated by teeth and 

 sockets, and the absence of an anus, place it among the Articulata. 

 The Terebratulidse are distinguished by an oval or rounded shell, 

 the structure of which is punctate, the dots corresponding with 



