58 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 84 



KEY TO THE SPECIES OF MICRODESMUS 



o'. Vent situated in posterior half of standard length. 



6'. Upper angle of gill opening opposite lower pectoral rays. 



c'. Dorsal 41 to 44; anal 2G to 29 ionthas 



c2. Dorsal 45 to 47; anal 30 to 33 floridanus 



6'. Upper angle of gill opening opposite or above base of middle 



pectoral rays. 



d^. Origin of dorsal fin less than one head-length behind head. 



e'. Dorsal fin supports 47; anal fin supports 26 to 30; origin 



of dorsal fin about two-thirds head-length behind 



tip of appressed pectoral aethiopicus 



e^. Dorsal fin supports 55 or more; anal fin supports 34 or 

 more; origin of dorsal above or before tip of appressed 

 pectoral. 



/'. Dorsal fin supports 55; anal fin supports 34 dipus 



p. Dorsal fin supports 69; anal fin supports 43 aflBnis 



<P. Origin of dorsal fin at least two head-lengths behind p^ 



head retropinnis 



a^. Vent situated in anterior half of standard length. 



6'. Body moderately elongate, head contained 8 to 13 times in 

 standard length; depth of body 10 to 20. 

 c*. Predorsal region contained 5 to 7 times in standard length; 

 dorsal 55 to 67; anal 38 to 48. 



d^. Depth about 20, preventral 10; dorsal 55; anal 38 hildebrandi 



d^. Depth 10 to 11, dorsal 67; anal 48 intermedius 



c*. Predorsal 8 to 9 times in standard length, dorsal 76; anal 



58 multiradiatus 



6'. Body very elongate, head contained about 15 to 17 times in 



standard length; depth 28 to 34 longipiiinis 



MICRODESMUS IONTHAS (Jordan and GUbcrt) 



Figure 9, b; Figure 10, a; Plate 2, Figure 1 



Cerdale ionthas Jordan and Gilbert, Bull. U. S. Fish Comm., vol. 1, p. 332, 

 1881 (1882) (Panama Bay). — Jordan and Evermann, U. S. Nat. Mus. 

 Bull. 47, pt. 3, p. 2449, 1898 (Panama). — Gilbert and Starks, Mem. 

 California Acad. Sci., vol. 4, p. 196, pi. 31, fig. 58, 1904 (Panama Bay). 



Body comparatively short, of nearly equal depth throughout, 

 strongly compressed posteriorly. Lower jaw strongly projecting, 

 with a small fleshy lump at the symphysis. Head 7.2 in standard 

 length; depth 8.5 to 9.2; predorsal 4.9 to 5.1; preanal 1.6 to 1.9; 

 caudal 2.2 to 2.4; preventral 7.2; base of ventrals to vent 2.6 to 2.9; 

 snout 5.4 to 5.9 in head, measured to upper end of gill opening; 

 interorbital 4.2 to 4.3. Dorsal 41 to 44; anal 26 to 29; pectoral 12; 

 ventral 1-3. Eye comparatively large, lateral, about equal to length 

 of snout; mouth small, oblique, not quite reaching to anterior edge 

 of eye; lips not notably fleshy, the lateral flanges small and incon- 

 spicuous; longitudinal ridges of snout and lower jaw well developed. 

 Teeth very small, close-set, in two irregular series in the jaws, vomer 

 and palatines toothless. Gill openings restricted laterally, the upper 

 end in front of lower pectoral ray, the aperture extending obliquely 



