686 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



Division OVICELLATA. 



The majority of species of American Tertiary Cyclostomata are provided with 

 ovicells and therefore belong to the division of the Ovicellata. Waters has pro- 

 posed the two subdivisions Parallelata and Kectangulata, which we have found 

 valuable in classification. The following key is introduced for the determination 

 of the families considered in this volume: 



KEY FOR THE DETERMINATION OF THE FAMILIES OF OVICELLATA. 



I The axis of the ovicell is perpendicular to the zooeeial axis LO (Rectangulata). 



' (The axis of the ovicell is parallel to the zooeeial axis 2 (Parallelata). 



The tul>es adjacent to the ovicell are not disarranged 3. 



The tubes adjcent to the ovicell are disarranged. The ovicell is formed 



before them 8. 



The ovicell is formed during the calcification of the adjacent tubes; 



! it is isolated 4. 



'' I The ovicell is formed after the calcification of the adjacent tubes and is 



supported upon them 5. 



JThe oeciopore is not different from the zooecia apertures Oncousoeciidae. 



'[The oeciopore is of different form Crisiidae. 



| The longer axis of the ovicell is parallel to the zooeeial axis G. 



| The longer axis of the ovicell is not parallel to the zooeeial axis 7. 



| The oeciostonie is terminal or subterminal Terviidae. 



' ]The oeciostonie is lateral Horneridae. 



| The ovicell is lobed (or lobate) Tubuliporidae. 



'' | The ovicell is not lobed Diaperoeciidae. 



The longer axis of the ovicell is perpendicular to the zooeeial axis 



(Orthogonal development) Plagioeciidae. 



The longer axis of the ovicell is parallel to the zooeeial axis 9. 



| A very large oeciopore is present (larva enormous) _.Macroeciidae. 



: ]Small oeciopore (ordinary larva) ._ Mecynoeciidae. 



jOvicell lobate (or lobed) Lichenoporidae. 



' | Ovicell noulobate (or not lobed) 11. 



(Ovicell not traversed by the tubes Leiosoeciidae. 



' |Ovicell traversed by the tubes 12. 



Ovicell flat Tretocycloeciidae. 



12. Ovicell globular, placed on the zoarial surface.- Ascosoeciidae. 



Ovicell placed between the fascicles Frondiporidae. 



The order of description of the various species is that of the geologic appear- 

 ance as known at present. 



Subdivision PARALLELATA Waters, 1887. 



The ovicell is developed parallel to the zooeeial axis between the tubes (and not 

 between the peristomies) . 



