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Show 286 SURGEON F. D A Y O N INDIAN SILUROID FISHES. [Apr. 4, Fig. ib. A single calice, fractured longitudinally, and exposing the deeply immersed and echinate columella, X 10 diameters. Ic. A calice viewed from above, displaying the "pit-like ' interseptal chambers produced by the lateral coalescence of the septa. 2. Stylaster asper, nat. size. .... _i • 11 2 «. Portion of a branchlet, enlarged 4 diameters, and exhibiting the thickly scattered ampulla?. . 3. Stenohelia maderensis, nat. size. Specimen from Madeira. 3 a. A small branch of an example from the Cape-Verde Islands, exhibiting thickly scattered " ampulla**." X 2\ diameters. 3 b Two terminal calices from the Madeiran example, viewed laterally, and showing an ampulla on the lower surface of the proximal one. s^s >~\ mfl*n"i(r***hp,Tra 3 c. A calice viewed ifrom above, showing the tendency of the lower edge to encroach upon and conceal the calicular fossa, a character which indicates its affinity with the genus Cryptohelia. 4. Amphihelia infundibulifera, nat. size. 4 «. Three calices, viewed laterally, X 6 diameters. 4 b. A calice viewed from above, illustrating the relative proportions of the septal elements. This figure is diagrammatic. PLATE XXV. Fi0-. 1. Allopora sidiviolacea, nat. size. 1 fl. Portion of a branch with calices, X 5 diameters. 2. Allopora explanata, nat. size. 2fl. Portion of a branch bearing calices and ampullre, X 5 diameters. 2 b. A single calice, X 25 diameters, exhibiting the pit-like interseptal chambers enclosing minute echinate secondary septa. 2 c. Portion of a calice in perpendicular section, displaying the stylate and echinate columella. 2. Notes on Indian Siluroid Fishes. By Surgeon FRANCIS DAY, F.Z.S., F.L.S. [Received March 20, 1871.] Amongst variations in the form of certain organs in fishes, the air-vessel furnishes some remarkable examples. In the genus Poly-nemus, amongst the Acanthopterygians, one species, the P. indicus, possesses this organ and appendages of such a size that it is collected in India for the isinglass it furnishes; whilst the P. tetradadylus does not possess even the vestige of an air-vessel. The existence of this organ in the marine and estuary forms of the Siluroid family is of some consequence in a commercial point of view, as most of the isinglass or fish-sounds exported from India to China comes from this source. The extensive order Physostomata of Miiller is chiefly based upon the existence of a communication between the air-vessel, when present, and the pharynx. Having lately had the opportunity of examining many species of freshwater Siluroids, or those forms which ascend long distances from the sea, I have made the following observations as to the presence or absence of air-vessels, and also the form they assume. In the 'Proceedings of the Zoological Society' for 1869, p. 309, I |