THE YELLOW LAMP-SHELL. 417 



OUR last example of the Pteropoda is the CYMBULIA, the large-winged animal placed 

 above the spike-shell. Though greatly resembling the carinaria in general appearance, 

 it is divided from that creature by many important structural differences. Its shell is 

 flexible, and in shape and translucency somewhat like the glass-slipper of fairy mythol- 

 ogy, the point, or toe, being set forward. Only three species of this genus are known. 



As group after group of molluscs passes before our notice, each seems to be more 

 extraordinary than its predecessor, and to present us with stranger and more unex- 

 pected forms. The molluscs of the next group are the first of the bivalves, but stand 

 alone in many particulars, and evidently form a transition between the gasteropoda and 

 the ordinary bivalves. They are all inhabitants of the sea, and, when adult, are found 

 attached to rocks, coral branches, and even other shells ; but in their earlier stages are 

 apparently able to swim freely through the water, as is the case with many other 

 molluscs. 



YELLOW LAMP-SHELL. - 



Terebratula flavesceas. 



(Open shell on right.) 

 PARROT-BILL LAMP-SHELL. Rhyachonella psittacca. 



SNAKE-HEAD LAMP-SHELL. 



Terebratula caput serpentis. 



GOOSEBlLL.Liugula aaatlna. 



In the ordinary bivalves, the two shells correspond with the right and leftside of the 

 animal ; but in the Brachiopoda, as these creatures are called, the one covers the upper 

 and the other the lower portion, and are called accordingly the dorsal and ventral valves. 

 Of these, the former is smaller than its companion, tJ which it is jointed by means of 

 certain interior sockets, which receive corresponding hooks in the ventral valve, and lock 

 them together so tightly, that they cannot be separated without something being broken. 

 The ventral valve is large, and is marked by a decided beak, not unlike the bill of 

 a parrot. In most instances the beak is perforated with a round hole, through which 

 passes the peculiar organ by which the animal attaches itself to the substance on which 

 it rests ; and when this is not the case, the hooked beak itself answers that purpose. 



In the interior is a rather complicated internal skeleton, a good example of which is 

 shown in the empty shell of Terebratula. The food is obtained in a singular manner. 

 The animal is furnished with a pair of rather long arms, covered with vibrating fibres 

 27 



