FISHES OF THE FAMILY LORICARIID. 199 
tentacles, the former have in addition a Y-shaped group of tentacles, the limbs of the 
Y starting in front of the nostrils and running forward to meet in the middle line on 
the upper surface of the snout (see Pl. XIV.). 
In Loricaria acuta and related forms the males are distinguished by the great 
development of the lower lip, which covers the entire under surface of the head behind 
the mouth. Steindachner, in describing L. spixii, states that this is due to the nursing- 
habits of the males, which are said to carry the eggs, during development, between the 
lower lip and the head. However, Dr. Siebenrock has kindly informed me that this 
statement was based only on the structure of the lip, which seems adapted for such a 
purpose, and that none of the specimens in the Vienna Museum show eggs in this 
position, 
In the Argiine the males are readily distinguishable by their elongate anal papilla. 
Changes during Growth. 
As in most Teleostean Fishes, the young have the head and eye proportionately 
larger than those of the adult, and as a general rule the head is relatively less broad, the 
snout shorter, and the interorbital space rather narrower in young specimens. In the 
Plecostomine the lower surface of the head and abdomen is naked in all very young 
specimens, and may remain so throughout life in some species, whilst in others a more 
or less complete covering of small granular scales may be acquired. In those species 
of Loricaria which have the abdomen covered in the adult with small granular plates or 
scales, the latter are acquired during growth in a similar manner. In the Plecostomin 
the dorsal fin is both higher and longer in the young than in the adult, the difference 
being very considerable in some species—e. g., in Plecostomus emarginatus the length of 
the base of the dorsal is equal to its distance from the adipose fin in small specimens, 
whereas in large ones it is contained 13 times in that distance. In the Loricariine the 
dorsal fin appears to become relatively higher during growth. Throughout the family 
the pectoral fin becomes relatively longer during growth, so that in the same species it 
may barely reach the base of the ventral in a small example and yet extend nearly to 
the posterior extremity in a large one. ‘There is no difference in the length of the 
pectoral in individuals of different sexes if they are of the same size. The length of 
the barbel is dependent on the size of the specimen; thus in Arges brachycephalus 
small specimens (80-110 mm.) have the barbel extending beyond the gill-opening, 
whilst in larger ones (200-220 mm.) the barbel extends only $ of the distance from its 
base to the gill-opening. 
Considerable changes of colour and marking may take place during the growth of 
certain species. In many Loricariine the young have 4—6 broad dark cross-bands 
on the back, which are absent in the adult. In the Plecostomine, in species such as 
Plecostomus guacari, P. verres, P. punctatus, &c., which have the head, body, and 
fins covered with dark spots, these are much fewer and larger on the head and body 
VOL, XVII.—PART 111. No. 2.—October, 1904. 25 
