LAEEO. 161 



when the mouth is closed, conceal the edge of the mouth, which in the allied 

 Varicorhimts is completely exposed. The lips vary greatly according to the species, 

 the two extreme types being shown by L. niloticus and L.forskalii. Looking into 

 the mouth, we notice that the upper side of the pharynx is occupied by a thick, 

 cushion-like, papillose pad *, in front of which, on the mucous membrane of the 

 palate, there is a group of large papilla? ; in L. niloticus, L. horie, and L. coubie these 

 large papilla? form a double series of lamellar transverse folds, which in their disposition 

 have been compared by Steindachner f to the cephalic disk of Echeneis. 



The scales are finely striated longitudinally, with or without a central area of 

 granular asperities. Narrow scales, agreeing in number with the fin-rays, form a sort 

 of sheath at the base of the dorsal and anal fins. 



There are 17 to 19 rays in the pectoral fin, and 10 (eight of which are branched) in 

 the ventral. 



The gill-rakers are short, but very numerous and closely set. 



The skull is massive ; a supraorbital bone is present, which is sometimes small and 

 always widely separated from the postorbitals ; the occipital crest is short and low and 

 does not extend on to the parietals, which bear a transverse ridge. The praemaxillaries 

 are devoid of ascending processes. The dentary bones are bent at an open or right 

 angle, the oral branch being perpendicular to the articular branch. The clavicles are 

 very strong, and bear an inward crest which restricts the passage between the pharynx 

 and the body-cavity, thus forming a kind of diaphragm. The numbers of vertebra? are 

 as follows in the specimens examined of the five species occurring in the Nile system : — 



L. niloticus 24 + 17 = 41 



L. horie 23 + 17 = 40 



L. coubie. . . . 21 + 14 = 35 



L. victorianus 21 + 15 = 36 



L.forskalii 23 + 16 = 39 



The intestinal canal is extremely elongate and much coiled up. According to 

 Heckel, its length equals eight or nine times the length of the body, but in a 

 specimen of L. forskalii measuring 170 millimetres I find the intestine measures 

 2640 millim., or sixteen and a half times the total length of the fish, and in a 

 specimen of L. coubie 230 millim. long it measures 4930 millim., or twenty-one times 

 the length of the fish. 



The fishes of this genus are essentially herbivorous ; they feed chiefly on alga? and 

 decomposing vegetable substances and also on diatoms and other minute organic 

 substances contained in the mud which they swallow in great quantities. Their 

 flesh, in Egypt, is absolutely worthless. 



* As exists also in the Carp, where it is known to epicures as the "toDgue." 

 t Sitzb. Ak. Wien, lxi. 1870, p. 562, pi. vii. fig. 1 a. 



Y 



