3402 



MOSS ANIMALS AND LAMP SHELLS 



UPPER VAI.VE AND ANIMAI, OF 



Crania (magnified). 



white, and the latter so transparent, that the calcareous framework and the promi- 

 nences on the valve are as easily seen as if there were no intervening mantle. 

 Externally, the shell is rarely white and smooth, being usually covered with plants 

 or animals which have attached themselves to it, and the valves perforated in all 

 directions, chiefly by boring sponges. 



The RhynchoneUida or beaked Brachiopods were extremely n,umerous in the 

 oldest geological times, but are now only represented by some three genera. The 



most important genus is Rhynchonella , which is one of 

 the oldest and most widely distributed of all known 

 organisms, being found from Silurian times through 

 all subsequent strata. The living R. psittacea shows 

 best the characteristic beak-like process of the ventral 

 valve; the aperture for the stalk being found under 

 this beak. The valves are fastened together as in the 

 Terebratulidce , but the calcareous framework consists 

 merely of two short, narrow plates, which are attached 

 to the smaller valve. Rhynchonella is not very numer- 

 ous in northerly regions, but empty valves are found 



in mud. Observations on the living animal are rendered difficult by the fact that it 

 is peculiarly sensitive to all disturbance, and closes its valves at the slightest 

 movement. The arm spirals widen sufficiently to allow the cirri to reach the edge 

 of the shell; the arms do not appear capable of un- 

 rolling and protruding beyond the shell. The mem- 

 bers of another family of this order of hingedBrachio- 

 pods, the Spiriferidce , are rendered very remarkable 

 by the long, spirally-coiled and calcified arms. 

 Spirifer was very abundant in the Paleozoic epoch, 

 but died out with the L,ias. 



The second order of the Brachiopods 

 Hingeless 



Group (Ecardines), or those whose shells are 



without hinges, consists of but four 

 families, two of which may be briefly described. 

 The unstalked genus Crania is widely distributed, 

 both geologically and at the present time. Its struc- 

 ture is so peculiar that it forms a family by itself 

 {Craniidce). The shell is attached to some sub- 

 marine object by the ventral valve; the dorsal valve 

 is lid-like, and the two valves connected, not by a 

 hinge or interlocking processes, but simply by 

 muscles. The best known of the four living species 



(here figured) of the northern seas, is almost always found in company with 

 Terebratulina, which, however, it does not follow into the seas of Northern America. 

 The last family to be described, the Lingulidce, is also one of the most in- 

 teresting. It existed in the oldest fossiliferous strata, and is still found living 

 chiefly near the shores of the warmer seas. It may be regarded as perhaps the very 



Lingula pyramidata. 

 (Natural size.) 



