FISHES OF THE FAMILY LOEICAEIID^. 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 PI. 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 Argiinae 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 

 Plecostominse 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 Plecostominse 

 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 emarginatiis 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 1^ times in that distance. In the Loricariinse 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 f of the distance from its 

 base to the gill-opening. 



Considerable changes of colour and marking may take place dur'ng the growth of 

 certain species. In many Loricariinee the young have 4-6 broad dark cross-bands 

 on the back, which are absent in the adult. In the Plecostominse, in species such as 

 Plecostomus guacari, P. verves, 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. xvu. — part in. No. 2. — October, 1904. 2 e 



