MUSEUM OF COxMPARATIVE ZOOLOGY. 108 



Behind its junction with the orbito-nasal the elongate suborbital makes 

 a prominent loop. A similar loop occurs in the subrostral in advance of 

 the nostril, and a second appears between the nostril and the median. The 

 nasal is not greatly curved; it joins the subrostral, which in turn unites with 

 the prenasal. Median and prenasals are short. The oral is crooked and 

 branched; it extends back between the branchial clefts of the first pair. Tu- 

 bules of moderate length, more or less branched, reach out upon the abdomen 

 Irom the jugular, and upon the posterior areas of the pectoral fin from the 

 pleural. 



Myliobatis freminvillci (Plate XLVIIL). Compared with the preceding this 

 Eay has a greater number of the pleural tubules massed together opposite the 

 spiracles, and fewer of them reaching out upon the body of the fin ; and it has 

 longer rostrals, orbitals, and prenasals. The scapular enclosure appears incom- 

 plete on its outer boundary. The occipital branch is connected with the long 

 occipital, and also with the lateral, possibly an individual peculiarity. Be- 

 neath the disk the areas enclosed by the pleural are more irregular, but the 

 oral is curved much more regularly. The nasal joins the subrostral, which 

 unites with the rostral. The orbito-nasal is short, being little more than a 

 crossing of nasal and angular. Subrostrals and prenasals are not united. 



Aetobatus. 



Aetobatus narinari (Plate XLIX.) has but slight scapular bends in the lat- 

 erals, and, apparentlj', has neither pre-scapular areas nor pre-scapular branches. 

 A post-scapular branch or two enclose a very small space. On the pleurals there 

 are few branches ; those that exist are long, reaching beyond the middle of the 

 fin. The branching.=5 of the tubules are similar to those of Myliobatis and its 

 allies. Opposite the end of the aural on each side is an occipital branch. 

 The occipital is long. A spiracular branch was not discovered on the orbital. 

 For a short distance this tube unites directly with the pleural, without the 

 intervention of tubules, as in most Batoids; it crosses the track of the crasial 

 twice, in front of the skull, and it descends not far from the tip of the rostrum. 

 The pleurals descend much nearer the fontanelle. 



The arrangement of the lower pleurals is similar to that of Myliobatis, 

 though the canals extend farther outward or backward ; they are hardly so 

 close together in front, but are closer to the jugulars along the branchial clefts. 

 From both of the transverse lines of the pleurals, near the forward edges ot 

 each pectoral, the tubules run toward the front; from the longitudinal portions 

 of the same tubes they pass outward, and from the binder part of the extension 

 from the jugular they reach inward. The suborbital and the angular meet 

 below the posterior edge of the orbit, whence a long orbito-nasal connects them 

 with the nasal and the subrostral. Both of the curves in the subrostral, that 

 in front of the nostril and that on the nasal flap, are sharp and prominent ; the 

 tube joins directly with the prenasal a little way in front of the median. As 

 is generally the case in the group, the median is rather short; the point at 



