scHucHERT.] DEVELOPMENT OF THE TELOTREMATA. 85 



they came in contact with hard objects during their growth, they 

 followed along or clasped the object of support. 



The sleuder shell-incased pedicle of the Strophomenacea probably 

 leads to the growth of long, straight hinges for additional sui^port, 

 further weakening the pedicle and necessitating accessory fixation in 

 four of its families, and finally occasioning in many species complete 

 loss of this organ at the maturity of the individual. With the excep- 

 tion of the Thecidiidai, the order Protremata has become nearly extinct 

 since the Jurassic era. 



TELOTREMATA. 



This order, though but 2 Cambrian and 20 Ordovician forms are 

 known, is represented by 766 species, or about 41 per cent of all 

 American Paleozoic brachiopods. It is as well developed specifically 

 as the Protremata, and exhibits a far greater variety of structures. 

 Telotremata was probably the last order to originate, and has the 

 greatest number and variety of living species. Its highest develop- 

 ment is in the Devonian, where 369 species in 50 genera occur, while 

 109 species are known from the Silurian, a growth more than five times 

 greater than that of the Ordovician system. Here, too, as in the 

 Protremata, considerable time was consumed in establishing a few 

 primitive characters, and these are no sooner obtained than an almost 

 sudden development of great specific and generic differentiation takes 

 place. 



It is highly probable that no telotrematous Paleozoic genus continued 

 to live through half the geologic time that Lingula and Crania did. 

 Ehynchonella, a primitive genus of this order, is often said to have 

 continued since the Ordovician, and Terebratula since the Devonian, 

 era. This is now very doubtful, since Hall and Clarke have demon- 

 strated that in all of the Paleozoic forms of these genera where it has 

 been possible to examine their interiors none belong to Ehynchonella 

 or Terebratula. In this catalogue both genera are recognized as occur- 

 ring in the Paleozoic, but this is due to the fact that the internal 

 structure of those species is not known. 



Telotremata has three distinct types of brachial supports, which 

 readily serve to differentiate 3 superfamilies. The simplest, Phyncho- 

 nellacea, has but crura, and is represented in the American Paleozoic 

 by 14 genera and 202 species, of which GG are widely distributed. The 

 superfamily Terebratulacea, having more or less simple V or W shaped 

 brachial supports, is present with 19 genera and 78 species, of which 

 23 are widely distributed. In the structurally more complex super- 

 family Spiriferacea, having spiral brachial supports, there are 41 genera 

 and 466 species, and of these 161 become widely distributed. This again 

 confirms the previously noted fact that the groups latest developed 

 have the greatest generic and specific differentiation. In Spiriferacea 

 this likewise occurred in the family Athyridse. 



