Bkkde.] Carboniferous Invertebrate*. 107 



to recognize but the one species, and think there is but little 

 doubt that his Spirigera caputserpentis is the same as the form 

 above described. The shells vary enough to easily include 

 Swallow's description. The microscopic indications of striae 

 mentioned in the various descriptions of this shell are probably 

 due to the fibrous structure of the shell, which is quite coarse. 



PELECYPODA 



Pelecypods (sometimes called lamellibranchs) are a group 

 of animals known under the names of mussels, clams, and oys- 

 ters. They live in fresh and salt water, and are covered by a 

 shell which is made up of two. halves, or valves. Brachiopods 

 have one valve on top and one on the bottom of the animal, but 

 the halves of the clam shell are located one on the right side 

 and one on the left. The body is nearly enclosed in a mantle 

 or fleshy membrane, which nearly surrounds the soft part of 

 the body. It is divided into two parts or halves, called lobes, 

 which secrete the two halves of the shell. Sometimes this 

 mantle is somewhat grown together for a large part of the way 

 along the lower sides of the animal near the open edges of the 

 shell. 



In those with the mantle edges fastened together there are 

 two openings in the rear end ; these openings are sometimes 

 prolonged into tubes called siphons, which are used in breath- 

 ing. A current of water passes constantly in through one of 

 these and out through the other. In those which do not have 

 the mantle united there is generally no siphon. 



The edge of the mantle is also attached to the shell, impress- 

 ing a line nearly parallel with the edge of the shell. When the 

 siphons are present there is an inward notch or angle in the 

 line in the back part of the shell, caused by the muscles used in 

 pulling the siphon into the shell. When the siphons are ab- 

 sent the notch is not present. The line formed by the edge of 

 the mantle is called the pallial line. 



Near the front of the shell lies an organ called the foot, which 



