96 BULLETIN OF THE 



Urolophus. 



Urolophus hallcri (Plate XXXVI.). A striking feature in this ray is the 

 absence of the post-scapulars. Their position is occupied by the pleurals and 

 by the pre-scapular branches. In the genera Raia and Rhinobatus the pleural 

 met the anterior of the scapular branches ; in tliis genus it is the posterior. 

 From the anterior part of the scapular curve there is a pre-scapular branch 

 which connects with the scapular, enclosing a small pentagonal area. Behind 

 the aural the laterals converge in a gradual curve until rather close together. 

 The aural is transverse. The occipitals are elongate and diverge forward. At 

 each end of the aural, on the laterals, there is a small occipital tubule with a 

 number of brauchlets. The pleurals run forward a little way outside of the 

 basipterygium of the fin; they pass under the suborbitals and go through close 

 in front of the skull. One or more tubules connect these tubes with the orbi- 

 tals. Laterally long tubules extend more than half the distance to the border. 

 At the fontanelle, the cranials make deep curves outward ; beyond this they 

 approach each other until nearly in contact at the tip of the snout. The orbi- 

 tal .sinks deeply into the tissue; at the outer edge of the spiracle a tubule is 

 sent backward, farther forward others pass out laterally, one or more uniting 

 with the pleural, and in front five or si.x long ones reach toward the front edge 

 of the disk. The tube passes down about midway from the fontanelle to the 

 end of the rostrum. 



Beneath the disk, on their appearance the pleurals run forward as far as 

 to the middle of the snout; thence they turn laterally and describe an arc of a 

 circle having a radius of about the distance between the first pair of gill open- 

 ings. This carries them back to a point opposite and near the coraco-scapular, 

 a point from which they pass directly to join the jugular e.xtension. Radiating 

 from the outside of the circle there are two- or four-branched tubules of me- 

 dium lenr'th. Emerrrins on the lower surface the suborbitals make a broad 

 sweep laterally, then turn back until behind the mouth, and then forward 

 toward the nostril till they meet the subrostrals. The connections of the short 

 orbito-nasal are similar to those of Isurus and the Holocephala, and not to those 

 of the majority of the Sharks. The angular is short, and reaches toward the 

 inner edge of the gill cleft. The jugular bends outward before running back 

 along the branchial apertures. No union is apparent between the rostrals and 

 the subrostrals. From the orbito-nasal the latter are transverse in general 

 course; they make a prominent bend forward in front of the nostril, and an- 

 other back upon the nasal valve, thence they pass forward at the side of the 

 prenasals, growing more and more delicate and transparent, and vanish before 

 reaching the middle of the snout. Individuals show the peculiar enlargements 

 or swellings in the tubes, in front of the median, that are seen in Potamotry- 

 gon. These rings or swollen portions closely resemble the follicles of Savi 

 They seem to be connected with the prenasals by the tissue of the walls, but 

 communication with the chambers of the tubes could not be discovered In 

 the nasals the curves are not very pronounced. The short median is hidden 



