DEVELOPMENT OF THE BRACHIOPODA 233 



The valves of Paterina [ Iphidea] are sub-equal, the 

 pedicle valve being a little more elevated than the brachial. 

 They are semi-elliptical in outline. In mature specimens 

 all lines of growth, from the nucleal shell to the margin, are 

 unvaryingly parallel and concentric, terminating abruptly at 

 the cardinal line. In other words, no changes occur in the 

 outlines or proportions of the shell during growth, through 

 the nepionic and neanic stages up to and including the 

 completed ephebic condition. The resemblance of this form 

 to the protegulum of other brachiopods is very marked 

 and significant, as it represents a mature type having only 

 the common embryonal features of other genera. It is of 

 further importance as representing, in many species, an 

 early condition of nepionic growth subsequent to the pro- 

 tegulum, during which the proportions and features of 

 the shell undergo no modification except increase in size. 

 This is termed the Paterina stage. It is well shown in 

 the brachial valve Orbiculoidea minuta Hall (Plate XI, 

 figure 5). * 



Modifications from Acceleration. The modifications in the 

 form of the protegulum are due to the influence of accelerated 



has been recognized as the type by C. D. Walcott (Bull. U. S. Geol. Surv., 

 No. 30, 102, pi. ix, figs. 1, 1 a, b, 1886). The species represented by Billings in 

 figures 347 and 349 resembles Obolus labradoricus (fig. 345, loc. cit.}, and is repre- 

 sented by Walcott (loc. cit., pi. ix, figs. 2, 2 a, b) and referred by him also to 

 Kutorgina. Mr. Walcott recognizes two groups of species, which are classified 

 (p. 102) as: "shell structure calcareous ( K. cingulata, K. Whitfieldi) or horny 

 (K. Labradorica, K. sculptilis) ." 



An examination of specimens representing both groups leads the writer to 

 consider Kutorgina cingulata and Obolus labradoricus of Billings as generically 

 distinct. Therefore the name Paterina is here proposed to include species of the 

 type of Obolus labradoricus, var. swantonensis. This name is intended to express the 

 primitive ancestral characters which it possesses (Plate XI, figs. 1,2). Exfoliated 

 specimens of Paterina labradorica show a roughened area on the cast, each side 

 of the median line near the beak. These probably represent muscular attach- 

 ments. Sections of the shell show no hinge-area as described in K. cingulata. 

 A study of the latter would doubtless present distinct stages of growth. The 

 dissimilar valves, arcuate ventral beak, and mesial depression could be developed 

 only by passing through several well-marked phases. This in itself seems 

 sufficient for a separation were no other characters present. [Walcott has 

 reinvestigated the genus Iphidea, and has decided that it includes the form 

 above designated as Paterina. Proc. U. S. Nat. Mus., XIX, 707, 1897.] 



