150 C. E. JBeeeher — Development of the Brachiqpoda. 



Preliminary to a study of the stages of growth observed in 

 the different orders, a simple characteristic example of each 

 will be taken to show the limitations of the post-embryonic 

 periods. 



Nepionic period. — In brachiopods, as in pelecypods, this 

 period represents the growth of the true shell immediately 

 succeeding the embryonic shell or protegulum, and before the 

 appearance of definite specific characters. In general, the 

 nepionic shells of all groups are marked only by fine concen- 

 tric lines of growth, and are therefore nearly smooth. Some- 

 times, however, a few radiating striae or other ornaments rnay 

 appear over the nepionic portion, but this is not the prevailing 

 rule. Obolus pulcher Matthew shows a cancellated nepionic 

 stage and is one of the most striking exceptional examples. 



Plate I, figure 1, represents the nepionic stage of Glottidia 

 albida, drawn from the beak of a well-preserved adult. The 

 shell at this period had a short straight hinge (originally the 

 hinge of the protegulum), with lines representing anterior and 

 lateral growth, making the outline broadly ovate. It is 

 divided from the succeeding growth of later stages by a strong 

 varix. The form is suggestive of Obolella, and as this is the 

 early form of growth of many of the Lingulidse and allied 

 families, it is here called the Obolella-stage. It is not 

 known that otherwise the characters agree with those of 

 Obolella, but as it is characteristic as well as descriptive the 

 name is used to designate this form of nepionic growth when- 

 ever present. 



The nepionic stage, of Orbiculoidea minuta, figure 4, shows 

 a continuance of the straight hinged condition after the com- 

 pletion of the embryonic shell, with nearly equal incremental 

 lines. As this agrees with the shell of Paterina it is called the 

 P at erina- stage. Trie pedicle emerged freely between the 

 cardinal margins of the valves. It will be shown thatboth 

 this and the Obolella-stage are represented in the nepionic 

 periods of many genera belonging to the Atremata. They 

 may succeed each other in a single species or one alone may be 

 present. In case both appear, the Paterina stage is always the 

 first one to be developed. 



The nepionic stage of Leptama {=Strophome?ia) rhomboi- 

 dalis, fig. 7, PI. I, is represented by a shell without radii, 

 having a comparatively large pedicle opening in the ventral 

 valve and a large deltidium. The hinge is not well defined 

 and the shell is discinoid in form. This term is not used to sug- 

 gest any special affinities with true discinoid genera, as Orbicu- 

 loidea or Discinisca. • The proper name for this stage is not 

 yet apparent to the writer. The external characters as ex- 

 pressed by both valves are manifestly nearer to Kutorgina 



