24 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I42 



The infraorbital canal in Albula and Pterothrissiis runs forward to 

 the anterior end of the lacrimal, where it doubles back and up into the 

 antorbital (see below). At its anteriormost point it is joined by 

 another canal which passes through two (Albula) or three {Ptero- 

 thrissiis) small (lateral rostral?) ossicles and then drops down into 

 the premaxillary, where it runs forward and ends blindly (fig. 7). 

 The canal in the premaxillary of Albula and Pterothrissus (it also 

 occurs in Dixonina) is unique among living teleosts. 



SUAN NA PH 

 I I 



LA LR PM 



Fig. 7. — Diagrammatic lateral and slightly superior views of the head of 

 Pterothrissus gissu (Clupeiformes). 



A, Showing the course of the sensory canals of the snout; B, showing the 

 superficial bones of the snout region (the course of the infraorbital system of 

 sensory canals outlined by dashes). 



AN, antorbital bone; CA, cavity in mesethmoid by means of which the supra- 

 orbital sensory canals of either side join; in, infraorbital sensory canal; LA, 

 lacrimal bone; LR, lowermost of the three lateral rostral bones; NA, nasal 

 bone; NO, nostril; pe, premaxillary sensory canal; PM, premaxillary bone; 

 PA'', prenasal bone ; so, supraorbital sensory canal ; SU, supraorbital bone. 



Halosaiiropsis (USNM 53615) is the only other fish known to the 

 author besides the elopoids that has small canal-bearing ossicles in 

 front of the lacrimal. Here, as in Albula and Pterothrissus, there is 

 a trough system of canals and a decidedly subterminal mouth. The 

 supraorbital and infraorbital canals end blindly forward. Just above 

 the premaxillaries on the lower surface of the snout there is a broad 

 cross channel which is only separated from the infraorbital canal on 

 either side by a membrane. Underlying the various canals in the 



