THE NAUTILUS. 51 



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, 1:!. 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 gpinnles. 



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 Truchyder- 

 mon; but the girdle is not that of True hyradsia nor Ischnochiton, 

 and the //ill-row i* short, extending forward only three-fourths the 

 length of the foot, as in 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 iii, iv, v, 2-1 ; 

 valves vi, vii, 1-1 slits, in the type specimen. 



ON THE AMERICAN SPECIES OF CYRENOIDEA. 



BY W. II. HALL. 



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 

 ' 'i/i'i'iioida. A little later in the same year, Deshayes reclaimed the 

 genus for his manuscript name of CyreneUa, which had been read to 

 the Societe Philomathique in December, 1834. The first published 

 name, corrected as above, has been adopted, in spite of the objection 

 to its formation 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 



