MUSEUM OF comparatrt; zoology. 97 



by cartilage. The prenasals diverge little from the parallel; they are discon- 

 nected forward. Behind the mouth, on each side, is a disconnected oral. 



The tubules of the back are more or less dissected into fine branchlets, 

 which form small groups about the ends. On the head the branchlets are 

 close together. Only the principal ones were sketched, but, when possible, 

 they were followed to their terminations. 



Urolophus torpedinus differs from U. hallcri mainly in matters of detail, in 

 tubules, etc. The specimen at hand has five of the enlargements, at the side 

 of the prenasal, in the subrostral; the tube ends with the fifth, seemingly 

 without other anterior connections, excepting by tissue from the walls. 



The junction of the pleurals to the anterior scapular branches in Ehinoba- 

 tus, and to the posterior in Urolophus, indicates that both may have been 

 secondary attachments ; in other words, that the attachment of origin in the 

 pleural is that with the orbital 



Taeniura. 



Tceniura lymma (Plate XXXVIII.) possesses both pre-scapular and post- 

 scapular branches. What is called the pre-scapular area in Urolophus and in 

 Dasybatus becomes, by the junction of the pleural tube to the middle of the 

 outer boundary, a scapular area in this form. Three of the long tubules on 

 the hinder part of the pectoral diverge from a single short stem, which con- 

 nects them with the pleural. After connecting with one or more of the orbi- 

 tal tubules, the pleurals go downward near the forehead. Immediately in 

 front of the prominent scapular curve the laterals approach each other closely. 

 They send out the occipital branch near the end of the aural. Along the 

 greater portion of their lengths they are studded with short tubules, the ma- 

 jority of which are branched two or more times, making four or more of the 

 branchlets. On the skull the extremities of the dissected tubules interfere with 

 each other so much, and become so confused, that it is not possible to present 

 more than an approximation in the sketch. 



An arrangement of the pleurals on the under surface intermediate between 

 that of Urolophus and Dasybatus is presented by this specimen. The lateral 

 curve of the tubes is not so round or so regular as in the former genus, and 

 the tubules are more massed along the anterior edge. Compared with the lat- 

 ter, the lateral sweep is more regular, and the tubules are much less crowded 

 along the anterior margin. From their point of appearance near the median 

 the pleurals describe curves which are entitled to rank as intermediates be- 

 tween those traced by the same tubes in the genera cited. At each end the 

 suborbital is bent so as to form a hook ; it meets the angular. Forward from 

 the nostril there is a deep fold in the subrostral; the tube does not return 

 quite to the nasal valve, and it cannot be traced beyond the base of the snout. 

 The nasal is moderately curved. There is a very short median, apparently 

 transverse. Behind each side of the mouth there is a short oral, which has 

 the appearance of being affected by the swellings elsewhere seen in subrostrals 

 VOL. XVII. — vo 2. 7 



