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 Eectangulata, 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. 
1 | The axis of the ovicell is perpendicular to the zooecial axis 10 (Eectangulata). 
' | The axis of the ovicell is parallel to the zooecial axis 2 (Parallelata). 
I 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. 
The ovicell is formed after the calcification of the adjacent tubes and is 
supported upon them 5. 
| The oeeiopore is not different from the zooecia apertures Oncousoeciidae. 
| The oeeiopore is of different form Crisiidae. 
| The longer axis of the ovicell is parallel to the zooecial axis G. 
'{The longer axis of the ovicell is not parallel to the zooecial axis 7. 
| The oeciostome is terminal or subterminal Terviidae. 
(The oeciostome 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 zooecial axis 
(Orthogonal development) Plagioeciidae. 
The longer axis of the ovicell is parallel to the zooecial axis 9. 
| A very large oeeiopore is present (larva enormous) Maeroeciidae. 
'(Small oeeiopore (ordinary larva) Meeynoeciidae. 
10 . 
Ovicell lobate (or lobed) 
Ovicell nonlobate (or not lobed) 
- Lichenoporidae. 
11 . 
(Ovicell not traversed by the tubes Leiosoeciidae. 
(Ovicell traversed by the tubes 12. 
( Ovicell flat Tretocycloeciidae. 
12. 1 Ovicell globular, placed on the zoarial surface Ascosoeciidae. 
Ovicell placed between the fascicles Froudiporidae. 
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 zooecial axis between the tubes (and not 
between the peristomies). 
