198 MR. C. TATE REGAN ON THE 



| Gen. XVI. Arges (con.). 
DAL whympert BlgT. eo iteas ber = resis. <) oi * | 
6; A. cigenMAnDL gn. -aecsir's o-ti 20 - * 
lhaty. “Ap -waillanty Peano. erties: + -ioa © Se aa 55 * 
16; Ajorientauncbigns semeiien > s s\si-bis)+ i> is i * 
| 9. A. brachycephalus Gtir. ..........;. Fc * | 
LO) RA Noted ehtatesteerisrerat ie ates int nye\-)-5,510"= * } 
11, (AS MAYMOYAUUS MEAN oe sclnin sn ols =e vos xe » | | 
ee Oe, os ee anne a Saw. is Fy | 
LBV ABB DAIO WIESE ss oa aldisvetns opieaiecy s nh ee te * | 
14. A. taczanowskil Blgr. ......--..-5.. rye ae) sis * 
LO; PAMVNOUBGIULASO. Gis a nesiet sofas «ssc * ) 
UG Pep SoM ARG. tee aisles s oy n.doin oie lele, e111 * ! 
DIT SRD NPLOREED SB UTS 3 fos cals yo. e pin le cieie vies a! 38 te te * 
RG WEA PEDUANUBOLEP. 5 50.0 sreis. tie voie oie love ln x 4 ate * 
PO SPASISUMNONSIL LLQM, | ein isis co's ofeleieisie woe * 
Gen. XVII. Astroprervs Humboldt. 
AS orixAl ys ZLIMIND.6.. 2% o's ci eile sila a ae 


Before passing to the systematic portion of this work, it may be as well to 
summarise the more important sexual differences and the changes which take place 
during growth. 
Sexual Differences. 
The differences between the sexes in certain genera are very remarkable. In the 
forms with the body protected by bony scutes it is often the case that the little spines 
which cover these and the plates of the head are stronger in the males than in the 
females. This feature is greatly exaggerated in Plecostomus spinosissimus and P. festa, 
in which the males have the head and body covered with quite strong spines. In 
other cases specialisation has resulted in the great development of spines or bristles in 
certain areas only. ‘Thus in Ancistrus setosus and its allies, and in many species of 
Oxyloricaria, Farlowella, and Loricaria, the sides of the head in the male are margined 
with bristles, which are either absent or considerably shorter in the female. 
In Loricaria lanceolata and its allies similar bristles occur in addition on the supra- 
occipital, the nuchal scutes, and the spine of the pectoral fin. In many species of 
Loricaria which have the sides of the head bristly in the males, the head is also some- 
what broader and the snout more obtuse in specimens of that sex, a feature which 
is perhaps more strongly marked in L. datirostris than in any other species (see 
Pi. YT). 
In most species of Xenocara the naked margin of the snout is much wider in males 
than in females, and whilst the latter have a more or less distinct marginal series of 
