Fishes of the Western North Atlantic 469 



series next on either side to median series hardly narrower transversely 

 than those of median series." 



marginata (Etienne G. St.-Hilaire) 18 17, (Isidore G. St.-Hilaire) 1827. 



Mediterranean and neighboring Adantic. 



3b. Anterior contour of cranium hardly concave; upper teeth of series next 



on either side to median series considerably narrower transversely than 



those of median series." peli Bleeker 1863. 



Tropical West Africa. 



Rhinoptera bonasus (Mitchill) 18 15 

 Figures 107, 108 



Study Material. Fifteen specimens, 238 to 250 mm (embryo) and 365 (newborn) 

 to 774 mm broad, and the head of a larger specimen about 1,500 mm broad, from 

 Woods Hole, Massachusetts; Newport, Rhode Island; lower Chesapeake Bay; Pensa- 

 cola, Florida; Main Pass, Louisiana; near Havana, Cuba; and Rio de Janeiro, Brazil; 

 in Harvard Museum of Comparative Zoology and in the U. S. National Museum. 



Distinctive Characters. The indented anterior contour of its cranium, with the con- 

 spicuously bilobed subrostral fin, marks this Ray off at a glance from all of its relatives 

 of the western Atlantic except for Rhinoptera hrasiliensis. R. bonasus resembles R. brasil- 

 iensis so closely in appearance and in bodily proportions that the two appear not to be 

 separable except by the number of teeth, of which there are normally only seven series 

 in each jaw in R. bonasus but nine in R. brasiliensis. Specimens with fewer series of teeth 

 or more and with less regular arrangement than normal are seen occasionally, bridging 

 the gap more or less completely between the two species. ^^ While the teeth of the median 

 series average shorter (anteroposteriorly) relative to their breadths (transversely) in 

 R. brasiliensis than in R. bonasus, the two species intergrade in this respect even within 

 the small series that we have studied. 



Description. Proportional dimensions in per cent of extreme breadth of disc. Female, 

 540 mm broad, and male, 774 mm broad, from Rio de Janeiro, Brazil (Harv. Mus. 

 Comp. Zool., Nos. 535 and 374 respectively). 



Disc: vertical length 55.0, 57.5. 



Snout length: in front of orbits 1.9, 1.2; in front of mouth 9.8, 10.3. 



Orbits: horizontal diameter 4.5, 4.4; distance between 10.7, 10.9. 



Spiracles: length 3.9, 3.2; distance between 14.6, 14.6. 



26. The tooth character used here as alternative between R. peli and R. marginata is derived from Bleeker's (Nat. Verh. 

 Holl. Maatsch. Wetensch., [2] 18, 1863: pi. i) original illustration of R. peli (description confusing) and from Du- 

 meril's (Hist. Nat. Poiss., i, 1S65: 64;) account oi R. marginata. Carman's illustrations of the teeth of R. marinate 

 (Mem. Harv. Mus. comp. Zool., 36, 191 3: pi. 48, fig. 4) veere of an embryo only 220 mm wide with the scar of 

 the yolk stalk still open, and from an unknown locality. It may not have come from the Atlantic. 



27. See p. 468, footnote 16. 



28. Our Study Material includes a R. bonasus from Rio de Janeiro, Brazil that has only six series and a R. brasiliensis 

 that has one of the lateral series suppressed on one side of the mouth in each jaw; but the presence of an extra series 

 on the other side of each jaw maintains the normal number (nine). Another abnormal specimen, with nine series 

 above but only eight below, has been reported from North Carolina (Radcliffe, Bull. U. S. Bur. Fish., 34, 191 6: 

 279. pl-47> fig- 4)- 



