The Latero-Sensory Canals and Related Bones in Fishes. 489 



by the side canal", and if this canal traverses this bone it would quite 

 certainly also traverse the more anterior cranial bones, though nothing 

 M'hatever is said as to this. What are apparently latero-sensory pores 

 are shown, in Traquair's figure, in certain of the cranial bones, and 

 those bones have dimensions and inter-relations that gives to the 

 dorsal surface of the head quite strikingly the appearance of that of 

 the holostean ganoids and but vei y little that of Acipenser. The bones, 

 as identified by Traquair, are in strict accord with their probable re- 

 lations to the sensory canals. Pores, it may be noted, are shown on 

 the parietal, the middle head line of pit-organs, which overlies this 

 bone in the holostean ganoids, thus apparently here being replaced by 

 a canal, as in Acipenser. 



In Osteolepis, which Zittel places in the Crossopterygidae, the 

 "Seitenporensystem ist am Kopfe (according to Pander [56, p. 16]) . . . 

 sehr entwickelt und die Mündungen der Eöhien odei- Kanäle äusserst 

 regelmässig in bestimmten Reihen, die gewöhnlich dem äusseren Rande 

 der einzelnen Knochen parallel laufen, gestellt". These pores, as shown 

 in the figures of Osteolepis macrolepidotus and Diplopterus borealis, are 

 all arranged in single lines, excepting those on the top of the anterior end 

 of the snout, where they are arranged in two or more parallel rows. The 

 general arrangement of the latero-sensory canals, as indicated by these 

 lines of pores, recalls somewhat that of the latero-sensory grooves in 

 Chaunax, the main horizontal line of the head, in both, forming, with 

 the supraorbital line, a confinons line, and not being in postorbital 

 communication either with the suborbital or with the preopercular 

 lines. In the occipital region of Osteolepis there is a supratemporal 

 canal which forms, with its fellow of the opposite side, a complete 

 cross-commissure, this commissure traversing three bones, a lateral one 

 on either side, and a single median one. These three bones are evi- 

 dently extrascapular, and they correspond exactly to the lateral and 

 median extrascapulars bones of certain specimens of Acipenser, and not, 

 as Pander concludes [56, p. 11], to certain post-extrascapular scales of 

 Polypterus. Anterior to these extrascapular bones, the main lateral 

 canal of Osteolepis traverses three bones which lie in a nearly 

 straight line along the lateral margin of the dorsal surface of the head. 



