FISHES OF THE FAMILY LOEICAEIID.E. 263 



9. Hypoptopoma. 



Hypoptopoma Giinth. Proc. Zool. Soc. 1868, p. 234. 



Oxyropsis Eigenm. & Eigenm. Proc. Cal. Ac. (2) ii. 1889, p. 39, and Occ. Pap. Cal. Ac. i. 1890, 

 p. 387. 



Body moderately elongate ; snout margined with recurved spines ; eyes placed very 

 low, equally visible from above and below ; interoperculum a plate on the lower surface 

 of the head ; temporal plate not perforate ; teeth slender, bifid. Dorsal above, or a 

 little behind, the ventrals, with I 7 rays, anal with I 5, pectoral with I 6, ventral 

 with I 5 ; caudal emarginate ; adipose fin, if present, represented by a feeble spine. 

 Vertebrae 5 + 6 + 15 (in H. guentheri) ; ribs absent. 



Amazon and La Plata Systems. 



• Key to the Species. 



I. Pectoral spine extending to middle of ventral ; abdomen with 3 longitudinal series of 



plates. 

 Depth of body 5^-5i times in its length ; caudal peduncle slightly 



compressed, 3i times as long as deep 1. H. thoracatum Gthr. 



Depth of body 7^ times in its length ; caudal peduncle depressed, 



7 times as long as deep 2, H. carinatum Stdr. 



II. Pectoral spine extending to posterior end of ventral or beyond ; abdomen with 2 series of 



plates, separated anteriorly by a single median plate. 



A. A transverse series of 4 plates in front of the clavicles. 



1. Caudal peduncle 3jr times as long as deep ; pectoral spine not extending to origin 



of anal. 

 No adipose fin ; length of head nearly 3 times in the total length (in 



a specimen of 65 mm.) 3. H. guentheri Blgr. 



An adipose fin ; length of bead 2| times in the total length (in a 



specimen of 78 mm.) 4. H.joberti Vaill. 



2. Caudal peduncle 2i times as long as deep ; pectoral spine 



extending to origin of anal 5. H. steindachneri Blgr. 



B. A single plate in front of the clavicles 6. H. i/vlare Cope. 



1. Hypoptopoma thoracatum. 

 Hypoptopoma thoracatum Giinth. Proc. Zool. Soc. 1868, p. 234, fig. 2. 

 Hypoptopoma bilobatum Cope, Proc. Am. Phil. Soc. xi. 1870 } p. 566, figs, on p. 567. 



Depth of body 5^—5^ times in the total length, length of head ?>\ times. Diameter 

 of eye 5^-6 times in the length of head, interorbital width 1^-lf times. Occipital 

 region evenly convex, without distinct median ridge. Scutes spinulose, not carinate, 

 23-24 in a longitudinal series. Lower surface of head with a naked area in front of 



vol. xvn. — part m. No. 10. — October, 1904. 2 n 



