THE NAUTILUS. Di 
the narrowly channelled and solid eaves, sharp and smooth. Slits 
in valve i, 16; valves ii to vii, 1-1 or 2-1 or 2-2, the larger num- 
ber prevailing on the more anterior valves; in valve viii, 13. Pos- 
terior tooth in the median valves square and well developed. 
Girdle rather unevenly covered, with convex, pebbly, coarse 
scales, those toward the outer margin elongated, and there is a 
copious marginal fringe of stout hyaline spinules. 
Gill-row three-fourths the length of foot, with 21 plumes on each 
side. 
Length about 14, breadth 8 mm. 
Unalashka (Dr. Benj. Sharp!). 
The number of slits is unusually great, and they are doubled in 
some valves; the girdle scales are coarse, the marginal fringe con- 
spicuous. These characters, together with the general smoothness 
of the valves externally, and the undefined, concave sinus, will 
readily distinguish the species. In view of its numerous slits, 
solid leaves and coarse girdle-scales, it is aberrant for a Trachyder- 
mon; but the girdle is not that of Trachyradsia nor Ischnochiton, 
and the gill-row is short, extending forward only three-fourths the 
length of the foot, asin the true Trachydermons. It has not the 
spongy eaves and sinus of Spongioradsia. 
The slitting of the intermediate valves is variable, but mainly 
Radsioid In valve ii there are 2-2 slits; valves iil, iv, v, 2-1; 
valves vi, vii, 1-1 slits, in the type specimen. 
ON THE AMERICAN SPECIES OF CYRENOIDEA. 
IBY W. “Heal: 
The genus Cyrenoidea was published in June, 1835, by de Joannis, 
in the Magazin de Zoologie; by a typographical error, apparently, 
the Latin form, which was used only once in the article, was printed 
Cyrenoida. A little later in the same year, Deshayes reclaimed the 
genus for his manuscript name of Cyrenel/a, which had been read to 
the Société Philomathique in December, 1834. The first published 
name, corrected as above, has been adopted, in spite of the objection 
to its furmation as a Latin name with a Greek suffix. 
The original type, C. Duponti Joannis, is from the Senegal River, 
West Africa, and it seems that his specimen was defective, since in 
