47S Mr. L. de Niceville on the 



and the longer anal fin with 15 to 17 rays. This genus is 

 founded on Oxydoras acipenserinus, Gthr., and 



Leptodoras juruensis. 



No teeth. Depth of body 9 times in total length, length 

 of head 5 times. Head 1^ as long as broad, covered with 

 skin, except on the occiput; snout depressed, pointed; poste- 

 rior nostril equally distant from the anterior and from the 

 centre of the eye ; eye in posterior half of head, its diameter 

 3 times in length of snout, equal to interorbital width ; 

 occiput and occipito-nuchal shield granulated and striated ; 

 bases of the six barbels united by the fold of the lower jaw; 

 maxillary barbel branched, not i length of head, not reaching 

 gill-opening ; latter extending to below centre of eye. 

 Humeral process striated, not ^ as long as pectoral spine. 

 Dorsal I 5, spine very feebly serrated in front, much pro- 

 duced beyond the soft rays, twice as long as head. Adipose 

 fin very small. Anal V 12, its base 2h as long as that of the 

 dorsal. Pectoral spine f length of head, reaching base of 

 ventral, with very strong serraj, especially on the inner side. 

 Ventral a little shorter than pectoral. Lateral shields 44, 

 not measuring \ the depth of the body, with serrated posterior 

 border and very strong hooked spine. Caudal deeply bifur- 

 cate. Brown ; pectoral, ventral, and adipose fins, and base 

 of dorsal and anal, blackish. 



Total length 235 millim. 



A single specimen formed part of a small collection made 

 in the Jurua River by Capt. Martins, and sent to me by 

 Dr. Goeldi. This collection contained besides examples of 

 two species not previously recorded from that river, viz. Pro- 

 chilodus insignis, Schomb., and Aphyocharax pusillus, Gthr. 



L. juruensis differs from L. acipenserinus in the more 

 elongate body, the smooth snout and opercles, the smaller 

 eye, the shorter maxillary barbel, the longer dorsal spine, and 

 the smaller lateral shields. 



LIX. — A Revision of the Pierine Butterflies of the Genus 

 Dercas. By Lionel de Niceville, F.E.S., C.M.Z.S., &c 



The name Dercas appears to have been a MS. name of 

 Dr. Boisduval's ; it first appeared in print in the ' Genera of 

 Diurnal Lepidoptera,' vol. i. p. 70 (1847), and was briefly 

 characterized, though not used in a generic sense, by Mr. 

 Edward Doubleday, to whom, therefore, the genus should be 

 credited, and not to Boisduval, as appears to have been more 

 generally the custom. 



