scHicHKRT] DEVKLOPMENT OF THE TELOTREMATA. 87 



at (lilVoioiit times and in separate pliyla straight caidina. areas are 

 more or less well developed. In America, the oldest members of this 

 OTi\Qr {ProtorkyncltK f minor and Z*. ." amb'ujtia, members of the family 

 Rhyuchouellidie) occur in the liower Cambrian. In these species, and 

 in the great majority of this family, there is no cardinal area; but 

 occasionally this character is ]»resent, the earliest conspicuous (;xami)le 

 being- the Ordovician genus Orthorhynchula. Among the Paleozoic 

 Terebratulacea cardinal areas are seldom developed. A (jonspicuous 

 exception, however, occurs in Tropidoleptus. But in the Mesozoic 

 and Ceneozoic, in the family Terebratellida', cardinal areas are very 

 ofteu present, and in living forms are accompanied by a short X)edicle. 

 It is, moreover, in the Spiriferiicea, the youngest superfamily of the 

 Telotremata to originate, that the greatest develoi)ment of cardinal 

 areas takes place. The oldest genera of the Spiriferacea are all ros- 

 trate, as in the Ordovician Zygospira, Catazyga, and Cyclospira. In 

 the Silurian the Spiriferida- tend to develop rapidly long, straight, and 

 wide cardinal areas, attaining greatest development in the Devonian 

 and early Carboniferous. This excessive development of cardinal 

 areas is no doubt due to the sliortening and decline of the pedicle, 

 since in the Triassic system forms occur in which cementation is com- 

 plete (Zugmeyeria and Thecocyrtella). Cardinal areas are also devel- 

 oped in other families of the Spiriferacea, but in no case can such be 

 traced to Ordovician lo-ng-hinged ancestors. 



In this order, more than in the Protremata, internal specialization of 

 the bracbia has progressed from a simple to a highly complex condi- 

 tion. In the Protremata, in its latest developed superfamily, Penta- 

 meracea, crura are also present, of the same phase of development 

 attained by the Ilhynchonellacea, tlie most primitive superfsimily of 

 the Telotremata. In this order, however, there are, with but few 

 exceptions, no internal special structures, as spondylia. The special- 

 ization in the Telotremata is expressed in the i)rogressive complica- 

 tion of the calcareous brachial supports. In the most primitive spe- 

 cies of the Rhynchonellacea no crura are present (Protorhyncha), but 

 in all later forms these appendages are well developed, and tinally in 

 the Trias and Jura attain very great length in Rhynchonellina. In 

 the next more complicated superfamily, Terebratulacea, the crura in the 

 primitive members have united anteriorly, thus forming the simple 

 unchanging loop of Centronella and Rensselneria, which is also known 

 to occur in the very young of some species of the highest superfamily, 

 the Spiriferacea. The geological history of the loop has shown that 

 the brachia have been constantly changing, causing more or less com- 

 plete resorption of the hard ])arts and adaptation to later requirements. 

 The progressive development of the loop is also repeated ontogenetic- 

 ally and more or less fully in living terebratuloids. 



In Zygospira, the oldest known genus of the suborder Spiriferacea, 

 the primitive loo[> of Centronella is reproduced in the earliest phase in 



