286 SURGEON F. DAY ON INDIAN SILTJROID FISHES. [Apr. 4, 



Fig. 1 b. A single calice, fractured longitudinally, and exposing the deeply 

 immersed and echinate columella, X 16 diameters. 



1 c. A calice viewed from above, displaying the " pit-like " interseptal 



chambers produced by the lateral coalescence of the septa. 



2. Stylaster asper, nat. size. 



2 a. Portion of a branchlet, enlarged 4 diameters, and exhibiting the thickly 



scattered ampullfe. 



3. Stenohelia maderensis, nat. size. Specimen from Madeira. 



3 a. A small branch of an example from the Cape- Verde Islands, exhibiting 



thickly scattered " ampullae." X 2i diameters. 

 3 b. Two terminal calices from the Madeiran example, viewed laterally, and 

 showing an ampulla on the lower surface of the proximal one. 

 X 5 diameters. 



3 c. A calice viewed from 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 infundibnltfera, nat. Bize. 



4 a. Three calices, viewed laterally, X 6 diameters. 



4 6. A calice viewed from above, illustrating the relative proportions of the 

 septal elements. This figure is diagrammatic. 



Plate XXV. 



Fig. 1. Allopora sitiviolaeca, nat. size. 



1 a. Portion of a branch with calices, X 5 diameters. 

 2. Allopora explanata, nat. size. 



la. Portion of a branch bearing calices and ampulla, X 5 diameters. 



2 6. 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. 



[Eeceived 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. tetradactylus 

 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 Midler 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 pre- 

 sence or absence of air-vessels, and also the form they assume. In 

 the 'Proceedings of the Zoological Society' for 1869, p. 309, I 



