Retort of the state Geologist. 



493 



perforated. Joubin has shown thai the deposits about the e< 

 and base of the muscular 

 bundles is without perfora 

 tions. The same is true of 

 all adventitious deposits in 

 punctate shells; senile en- 

 largements of the teeth and 

 cardinal process, the callosi- 

 ties in the delth.3 num. as 

 in Spirifer. and the syrinx 



in SyBTNGOTHYBIS. W tether F , G 9 ,. _ Y ert ; ca [ sec tion of an attached valve of 



the teeth and other articil- Crania, showing the normally perforate shell, find 



, . the imperforate deposit beneath the muscular scar 



Latmg apophyses are 1111- (Jovlv 



punctate in their earlier condition, has not been determined; 

 The calcareous secretions in the brachia (spirals, loops, etc..) are 

 also impunctate. 



As to the function of the punctae, it is quite generally believed 

 that they are connected with the respiration of the animal. In 

 recent punctate species the tubules are filled 

 by diverticula from the mantle, which are 

 readily seen by dissolving the shell of a 

 terebratuloid in dilute acid. The fact, how- 

 ever, that they are not exposed to the water 

 at their extremities may interfere with this 

 interpretation, unless an increased exposure 

 be effected by the access of water from 

 within the body chamber. It has been 

 observed by Morse that the punctae in 

 Terebratulina appear only after the shell 

 has passed its earliest growth-stages. 



THE ANIMAL. 



General Characters. 

 Upon opening the valves of a living brachiopod, the body, or 

 that part of it which contains the essential organs, is found 

 to be restricted to the posterior part of the internal cavity, 

 while the anterior one-half or two-thirds of this space is rilled 

 by the coiled arms from which the name of the class is 

 derived. The degree to which the valves can be voluntarily 

 opened by the animal is very restricted, only sufficient to freely 



45 



Fig. 97. — Extremities of 

 the shell perforations in 

 Crania.— (Joubin). 



