808 EEPOET OF COMMISSIONEK OF FISH AND FISHERIES. [62] 



beiug the only one lie had in his possession. 1 chose these two crania, 

 from which I made the drawings that illustrate this essay, because we 

 find in the organization of both Alhula and Megalops at least one feature 

 that they possess in common with Amia. In Alhula it is the peculiar 

 structure of the bulbus arteriosus and in Megalops the presence of the 

 gular plate. But in describing the crania of these two forms I will con- 

 fine myself strictly to the two specimens in question, and only describe 

 what is to be seen in them. The sequel will prove that there is much of 

 interest and importance. Judging from the cranium alone, the complete 

 dissection of Alhula will well repay the anatomist some day, for this part 

 of its skeleton presents many points of the greatest interest and diver- 

 sity in development. 



There is but this one species of Alhula known to science, and its prin- 

 cipal habitat are the warm tropical seas, where it is abundant. With 

 us, however, it has been taken from Cape Cod clear around to Southern 

 California (Jordan and Gilbert.) This fish, we are told by the authors 

 just quoted, possesses "no gular plate." 



Viewing the cranium of Alhula from above, and proceeding with our 

 examination from before, backwards, the first object that strikes us is 

 the extraordinary ethmoid it possesses. (Plate XII, Fig. 30, Etli.) 



This bone is fashioned ofi" in front so as to remind^ one very much of 

 the snout of a pig. From this part it extends backwards in a median 

 crest, deeply grooved above. This runs in between two prolongations 

 developed by the frontals, and can be seen opposite the letters ISTa^ in 

 Fig. 29. Anteriorly the ethmoid projects over the parasphenoid, which 

 bone abuts against it. From the base of its median crest it sends 

 downwards and outwards on either side a plate-like portion, the mar- 

 gins of which curl up for their posterior moiety. A vacuity of an ellip- 

 tical outline exists in the crest anteriorly as it reaches the snout-like 

 protuberence, and only the grooved part is carried over to meet this por- 

 tion of the bone. This foramen can only be seen upon a lateral view a» 

 shown in this figure. 



The frontals (Plate XIII, Fig. 30, Fr.) are very extensive bones and 

 cover nearly the entire superior aspect of the cranium. Their union 

 with the ethmoid is of such a nature as at first to give one the impres- 

 sion that the two arebutoue bone, and indeed the suture between them 

 is not always discovered at once. Just above the prefrontals, bones 

 which they overshadow all to their outstanding wings, they present on 

 either side of the extension of the ethmoidal crest the openings of 

 two very large mucus canals. These open behind in slit-like foramina, 

 just beyond the letters Fr. (Fig. 30), as well as in more minute open- 

 ings behind and to the outer side of them. The frontals completely 

 overarch the orbits, lap down upon the postfrontals and squamosals, 

 while posteriorly in this specimen the left-hand bone appears to overlie- 

 the fellow of the opposite side as well as both the parietals. Thes& 

 latter bones are comparatively small plates of a quadrilateral outline^ 



