526 ' PROCEEDINGS OF THE NATIONAL MUSEUM vol. 83 



in the subgenus Madeayina). Extra plates on top for support of 

 dorsal usually two, var;7ing one to three; usually on first caudal and 

 last trunk segments, sometimes also on penultimate trunk segment, 

 sometimes either on last trunk or on first caudal segment only. Upper 

 ridge of trunk discontinuous with upper ridge of tail, the two ridges 

 usually overlapping on two segments, varying one to three, on those 

 segments having extra plates for support of the dorsal. (For a full 

 discussion of the correlation between the extra plates, the modified 

 segments, and the overlap of the ridges, see pp. 505 to 507.) Median 

 ridge of trunk continuous with lower ridge of tail ; lower lateral ridge 

 of trunk ending on last segment ; midventral ridge of trunk ending on 

 penultimate segment. A lateral expansion or wing extending from 

 lower plate of last trunk segment, converging with its fellow from the 

 opposite side and uniting behind bnse of anal fin. Points of inter- 

 section of transverse and longitudinal ridges bearing pointed spinous 

 processes in the very young, usually persistent as short tubercles in 

 grown specimens, in some species becoming nearly obsolescent or 

 reduced to low stumps, the tubercles usually somewhat better devel- 

 oped in females. Lateral line present, indicated by a series of paired, 

 minute, pimplelike appendages, each pau' forming tiny lips for a 

 minute slitlike pore; a pair of lips on transverse ridge of each segment, 

 the series of pairs arranged regularly in a nearly straight longitudinal 

 line, running on trunk nearer to median lateral than to upper ridge 

 continued in a nearly straight line on the tail, situated there nearer 

 to upper than to lower ridge. Appendages on tubercles and coronet 

 often present, often branched, often altogether absent, depending on 

 individual variation and to a certain extent on age and on the species 

 (see p. 510). 



