236 SILUKIDJE, 



or eight scutes between the two dorsal fius. Dorsal a little higher 

 than long, the length of its first ray being a little more than that of 

 the head. Caudal fin obliquely subtruncated ; its outer rays are not 

 spiny, and the lower is longer than the upper ; there are twelve 

 scutes between the anal and caudal. Pectoral spine very strong, 

 armed above with numerous long curved spines ; it extends back- 

 wards to the second third of the length of the ventral. The scutes 

 of the body are striated, but not keeled, and the posthumeral ridge 

 is rather obtuse. All the fins with numerous black dots, which are 

 only one-half or one-third as large as the eye, forming three irre- 

 gular series in each intcrradial space of the dorsal fin, and two in 

 each of the caudal. 

 Brazil. 



a-b. Fine specimens, 10 inches long. Bahia. From Dr. 0. Wu- 

 cherer's Collection. 



11. Plecostomus robinii. 



Cm. 6f Val. xv. p. 501. 



D. 1/7. A. 5. P. 1/6. L. lat. 26. 



Head depressed, with scarcely any prominence on the occiput and 

 nape, its length being one-third of the total (without caudal) ; no 

 ridge between eye and nostril. Snout broad, subsemicircular, with 

 its extremity somewhat thickened, and naked in the middle ; labial 

 fold of moderate width, not notched behind. Interoperculum with- 

 out any spines. Thorax and beUy entii-ely naked, there being only 

 a few minute granulations between the labial fold and the gill- 

 opening. Dorsal fin rather longer than high, the length of its base 

 being more than its distance from the second fin. There are seven 

 scutes between the two fins. Caudal obliquely emarginate. The 

 pectoral spine extends to the base of the ventral, and has its extre- 

 mity covered with very short bristles. Fourteen scutes between 

 anal and caudal ; the lateral scutes of the body without keels or 

 prominent spines ; posthumeral ridge very obtuse. Head, body, and 

 fins with round black spots, those on the head being much more 

 numerous and considerably smaller than the others ; the spots on 

 the body are arranged in about five longitudinal series ; only one 

 scries on each intcrradial space of the dorsal fin ; the spots of the 

 caudal fin form six transverse series. 



South America; (Rio de la Plata, Trinidad*). 



a. Fine specimen. Bahia. From Dr. 0. Wucherer's Collection. 



* Trinidad appears to be inhabited by a species with the scutes keeled ; it lias 

 been described by Mr. Gill under the name of Hi/postomus rohinii, but is evi- 

 dently different from oiu* species (Ann. Lvc. Nat. Hist. New York, vi. p. 46). 



