MUSEUM OF COMPARATIVE ZOOLOGY. 79 



forward. The subrostrals are moderate in length and slight in curvature. 

 The nasals are transverse, broadly curved forward between the nasal valves. 

 Approaching the symphysis, behind the corners of the mouth there is a pair 

 of detached orals. A short median and moderate prenasals, the latter con- 

 nected with the rostrals, complete a system closely resembling that of Mustelus 

 and with remote likenesses to that of Scylliorhinus. 



An embryo of two and a half inches agrees so well with the adult that it 

 is readily identified by means of the canals. Without the aid of the system 

 identification would hardly have been possible. 



Isurus. 



Isurus punctatus (Plates I., X.) by the fusiform shape of its body compels 

 the laterals to diverge considerably along the middle of the flanks. With this 

 exception they are tolerably straight, there being hardly any deflection above 

 the anal, and but a scarcely noticeable upward turn on the tail. In reality the 

 laterals cross the muscular portion of the tail, not following the course of the 

 vertebrae, and they end at the lower (hinder) edge of the muscles close behind 

 (above) the lower caudal lobe in front of the concavity in the posterior margin 

 of the fin. 



The aural is long, without prominent curves. The occipital is short, and 

 nearly transverse. Both coronal and rostral curves of the cranials are long 

 and shallow. The rostrals are short. In its downward course the orbital is 

 waved a little; as a suborbital it joins the subrostral below the forward margin 

 of the orbit. By its connections the short orbito-nasal would appear to be 

 reversed in direction. In one specimen the angular bends downward behind 

 the angle of the mouth to meet the oral, and the jugular makes an upward 

 turn, then goes half-way to the gill, to bend up still farther at the end; in an- 

 other case the angular and jugular form a single nearly straight line. The 

 oral is connected with the angular, and runs but little beyond the corner 01 

 the mouth. At less than a quarter of the distance from the eye to the rostral 

 tip, the subrostral appears on the lower surface; from this point it is longitudi- 

 nal, faintly curving above the nostril. No nasal curve appears in the nasals. 

 The short median is nearly transverse. About one third of the prenasal is 

 bent abruptly to the side to meet the rostral. 



Prominent among distinguishing characters are the caudal portions of the 

 laterals, the reversed orbito-nasal, the transverse median, the curveless nasal, 

 and the attached oral. 



Odontaspis. 



Odontaspis americanus (Plate XI.) exhibits neither scapular nor anal curves 

 in the laterals. The canal remains near the middle of the tail, and stops a 

 little forward of the last of the vertebras. 



The aural bends back in the middle a very little. The occipital is of mod- 



