62 BULLETIN OF THE 



come the rostrals (r), and after passing below the snout they are known 

 as suhrostrals (sr). At the end of each cranial, on the crown of the head, 

 an orbital (orb) canal runs outward behind the orbit ; below the eye, 

 and below the disk in the flat-bodied Selachians, they become the sub- 

 orbitals (so). A transverse tube from one lateral to the other, close to 

 the external openings of the aqueducts, ear openings as commonly 

 named, is the aural (au). A short occipital (oc) reaches from the aural 

 to the orbital ; or, in other words, from the lateral to the cranial. 



On the ventral surface the canal passing lengthwise near each angle 

 of the mouth is the angular (ang). The portion to which this name 

 is applied is not a long one ; farther back on the same tube, the name is 

 supplanted by that o^ jugular (j). In some cases these canals are 

 definitely limited by a branch, the oral (o), putting out transversely 

 behind the mouth; but very often the oral is found to have lost its con- 

 nection with the other tubes. Earely the oral is continuous across the 

 symphysis. In front the angular meets either the suborbital or a canal, 

 the nasal (71), extending behind the nostril, between the latter and the 

 mouth ; sometimes the one is met, sometimes the other ; whichever it 

 may be, it marks the anterior limit of the angular. The two nasals 

 meet in front of the middle of the mouth, in most cases, and, unit- 

 ing, form a short median (m), from which two other tubes, the pre- 

 nasals (p«), diverge and run forward to the end of the snout. On a few 

 forms the nasals do not meet. In some instances there is a junction of 

 subrostral and nasal ; in others, the subrostral joins tJie suborbital ; in 

 one species the angular and the nasal join, in another it is the angular 

 and the suborbital ; but however the junctions may be arranged, a tube 

 of less or more extent lies between the end of the orbital and that of 

 the nasal. Its position is indicated in its name, orhito-nasal {on). 



BATOIDEI. 



If one of the round-bodied sharks were to be greatly depressed and 

 flattened, extension taking place on both dorsal and ventral surfaces, 

 the pectoral fin at the same time being expanded and applied to the side 

 of the trunk, the arrangement of the main tubes of the system would 

 be similar to that obtaining on the Batoidei. The subrosti-al, nasal, 

 prenasal, angular, jugular, and suborbital would appear on the lower 

 surface, as in the Skates and Rays. An important addition to what has 

 been recorded in the Galei occurs in the Batoidei : a pleural canal {jil), 

 which meets the lateral at the shoulder, runs outward on the pecto- 



