NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
393 
„ f Exterior aperture transverse and mucronate 6 . 
'[Aperture elliptical 7 . 
| Two small lateral avicularia H. transversora. 
'[Two large avicularia below the aperture //. ligulata. 
[Avicularia very small; zooecia hexagonal H. pungens. 
* ' \ Large avicularia 8 . 
8 . 
Lower face smooth or tubercular, two large avicularia H. alifera. 
Lower face of the zoarium perforated; one large and one small aviculariuim/L radicata. 
,'No mucro 
Q 1 
' [ Mucro present 
[Peristome thin; two large avicularia, ovicell smooth 
10 . 1 Peristome thin; one submedian avicularium, ovicell with small pores. 
I Peristome very thick; two or three small avicularia; ovicell smooth___ 
[Two large avicularia. 
11I 
'[Two small avicularia 
12 . 
Enormous mucro with pallet; three rows of areolae. 
Small mucro; tuberosities radial on the frontal 
._] 0 . 
- 11 . 
II. alifera. 
11. punctata. 
If. crassicollis. 
H. ligulata. 
12 . 
..H. axiculata. 
^H. tuberose. 
Genus HJPPODIPLOSIA Canu, 1916. 
1916. Hippodiplosia Canu, Les Bryozoaires du Sud Ouest de la France, Bulletin Societe 
Geologique France, ser. 4, vol. 14, p. 326. 
The poster is nearly, as large as the anter. The operculum is somewhat nar- 
rowed laterally at the site of the cardelles. The operculum always closes the oricell. 
which is hyperstomial. The frontal is a tremocyst. There are some spines and 
some avicularia. 16-18 tentacles. 
Genotype. — Hippodiplosia ( Eschara ) pallasiana Moll, 1803. 
Range. — Jacksonian-Beeent. 
In this genus the vanna is very large; it is the opening of a compensation sac, 
probably larger than in Hippoporina Neviani, 1895. Consequently the tentacles 
ought to be more numerous or larger. Calvet reports 16 to 17 tentacles in the 
genotype. On the other hand, one can suppose that a larger vanna permits simply 
more rapid egress of the tentacles as an immediate compensation, since the com- 
pensatrix is smaller in this group than in Schizoporella. 
The Eocene species of the genus are rather different from those of the Miocene. 
Tt is probable that when the physiology of the avicularia is better known some 
restrictions will be necessary. 
The living species of this genus are : 
Hippodiplosia (Eschara) pallasiana Moll, 1803. 
Hippodiplosia ( Lepralia ) res tit a, Hincks,. 1885. 
The fossil species are ; 
Hippodiplosia ( Lepralia ) rarepuncta Reuss, 1817. Tortonian. 
Hippodiplosia (Lepralia) planiceps Reuss, 1817. Tortonian. 
Hippodiplosia (Lepralia) semicristata Reuss, 1817. Tortonian. 
Tiippodiplosm (Lepralia) clavata Manzoni, 1871. Tortonian. 
Hippodiplosia (Lepralia) auingeri Reuss, 1817. Tortonian 
