DEVELOPMENT OF THE BRACHIOPODA 243 



tremata comprises the Kampylopegmata and Helicopegmata 

 of the same author. With the transfer of some genera in his 

 sub-orders, they may be properly recognized and serve further 

 to differentiate the class into comprehensive groups. 



After this preliminary discussion the four groups pro- 

 posed can be defined and understood. The special details 

 with full illustration and demonstration of the development 

 and affinities in each group are left for future consideration. 

 At present it is aimed to give only the general results which 

 have been reached through the study of individual develop- 

 ment (ontogeny) among various species representing the 

 families of nearly the entire class. Of the sixteen families 

 of Brachiopoda recognized by (Ehlert in Fischer's " Manuel 

 de Conchyliologie," fifteen have thus been studied and deter- 

 mined. The genera marked by an asterisk have been exam- 

 ined somewhat in detail. The others have been investisrated 

 partly from adult specimens, and from the published descrip- 

 tions of the genera. 



ATREMATA. 



(a priv., and rprj/ia perforation.) 

 (Plate XI, figures 1-4.) 



Protegulum semi-circular or semi-elliptical ; hinge-line 

 straight or slightly arcuate. Growth taking place mainly 

 around the anterior and lateral margins, never enclosing or 

 surrounding the pedicle, which in all stages emerges freely 

 between the tAVO valves, the opening being more or less shared 

 by both. Valves inarticulate. 



Including the genera : 



Dignomia. *Leptobolus. Obolics. 



Dinohulxts. *Lingula. *Iphidea. 



Elkania. Lingulasma. Paterula. 



Glossina. *Lingulops. Rhynoholus. 



*Glottidia. Monomerella. Trimerella. 



Lakhmina. Obolella. 



