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Show 286 ME. W. E. COLLINGE ON THE [Apr. 2, It continues through the squamosal into the sphenotic and in the region of pore number 7 divides into two branches, viz. the supra-and sub-orbital. The Supra-orbital Branch passes through the sphenotic into the frontal and makes a sharp turn to the region of pore number 9 (PI. X I X . fig. 6), and then in an outward curve passes around the anterior nasal opening, where it terminates. The Sub-orbital Branch passes posterior and ventral to the orbit in the sub-orbital bones, opening in its course by three pores. In the specimens I examined, the operculo-mandibular branch differed from that figured and described by Pollard (11. p. 534) in that there is a distinct mandibular portion. It is not connected with the main canal of the head, but arises near the head of the preoperculum, through which it passes ; opening by three pores it passes into the mandible, in which portion there is a single pore, number 4 (PI. X I X . fig. 6). The species examined by Pollard was C. paleatus. If the condition figured by this author is correct for the adult stages of G. paleatus and Trichomgterus tenuis-he examined only young forms of both-they are very interesting, and offer perhaps the simplest type of sensory canals in tbe Physostomi. III. CYPBINIDjE. LABEO DUSSUMIEBI. I do not propose to describe tbe sensory canal system in Labeo, but wish to draw attention to the presence in this family of a series of sense-organs which, so far as I can learn, are peculiar to it. Valenciennes x was the first, I believe, to make any mention of them, and later Bleeker2 pointed out their presence. Neither of these authors described their structure, which w7as first detailed and figured by Leydig (8) in the thorough and careful manner characteristic of all this author's work3. It is rather singular, but I cannot find a single reference to this very important paper in any of the writings of recent workers upon the subject. In Labeo there are distributed over the anterior region of the head and around the borders of the mouth a large series of pores of different sizes with overlapping edges standing above the level of the skin. These edges are quite smooth and unpigmented (PI. X I X . fig. 7). Each pore leads into a flask-shaped cavity varying in size according to the size of the pore (PI. X I X . fig. 8). The latter average from 1 to 3 millim. in diameter in Labeo dussumieri, the cavity being from 3 to 10 millim. in depth. From the 1 Cuvier et Valenciennes, Hist. Nat. des Poissons, 1842, vol. xvi. 2 Bleeker, Atlas ichthyol. d. Indes-Orientales Neerlandaises, 1863, t. iii. 3 The species described by Leydig are Schismatorhynchus heterorhyiwhus, Blkr., Lobocheilus falcifer, van Hass., and Eohita vittata, Val. Bleeker makes mention of their presence in various species of the following genera:- Crossocheilus, Labeo, Lobocheilus, Schismatorhynchus, Epalzeorhynchus, Eohita, Diplocheilichthys, Morulius, and Danzila. |