858 Rev. T. Hincks on the Genus Retepora 
b. Without an oral fissure. 
3. Retepora plana, n. sp. (Pl. XVIII. figs. 7, 8.) 
Zoartum thin, flat, and compressed. Fenestre rather large, 
usually pointed above and below, separated by wide inter- 
spaces (three or four rows of cells) ; habit of growth unknown. 
Zooecia ovate, very slightly convex, surrounded by a raised 
line, surface smooth ; orifice arched above, with a straight lower 
margin; peristome not raised, thin, entire, unarmed; fre- 
quently a small avicularium, with rounded mandible, imme- 
diately below the mouth, usually supported on an umbo. 
Dorsal surface smooth, vibicate, destitute of avicularia. 
Oocecia ? 
Locality. Red Sea (probably). The specimens form part 
of the collection to which I have previously referred. 3 
This very distinct species is characterized by the flatness 
and evenness of its surface, by its great simplicity of structure, 
and the slight development of the accessory appendages, 
which are usually so abundant amongst the Retepores. The 
cell resembles that of an ordinary Lepralia (auct.). The 
orifice is well arched above and straight below, the height 
somewhat exceeding the breadth, and is surrounded by a per- 
fectly simple peristome, which is not raised above the level of 
the surface. 
The small rounded avicularium, which is often present 
below the mouth, usually mounted on an umbonate rising, is 
the only appendage which occurs in my specimens. 
4, Retepora tessellata, n. sp. (Pl. XTX. figs. 9-12.) 
Fenestre elongate, narrow, not so wide as the interspaces, 
which are broad and rather massive; habit of growth un- 
known. Zooecia short-ovate, smooth, flattish, bordered by 
a raised line ; orifice arched above, lower margin straight, with 
a small central sinus, the front wall (in the adult state) carried 
up on each side of it and terminating above in a somewhat 
pointed extremity, hollowed out below it ; a spine immediatel 
above each lateral prolongation of the front wall; usually on 
the front of the cell a slender elongated avicularium with pointed 
mandible, frequently placed transversely, but sometimes 
directed downwards ; many stout processes distributed over 
the zoarium, standing out at right angles to its surface, and 
bearing a large pointed avicularium on one side. Oowcéa im- 
mersed, subglobose, smooth, hollowed out in front. Dorsal 
surface divided into numerous distinct areas, bounded by raised 
lines, each bearing one or more of the elongate avicularia. 

