440 Memoir Sears Foundation for Marine Research 



of pectorals less than distance between inner ends of first pair of gill openings in M. 

 freminvillii (as great or greater than distance between first gill openings in M. goodei of 

 all sizes). Although the subrostral lobe averages longer in M. freminvillii,^*^ there is no 

 actual discontinuity between the two species in this respect in the one sex (female) for 

 which comparison has been possible. Other differences between M. freminvillii and 

 M. goodei, supposedly alternative, such as relative size of eye and of teethes and breadth 

 of pectoral flange below eye, have not proved so. 



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

 650 mm broad, from Provincetown, Massachusetts (Harv. Mus. Comp. Zool., No. 

 992). Male, 761 mm broad, from Rio de Janeiro (Harv. Mus. Comp. Zool., No. 396). 



Disc: vertical length 57.3, 63.1. 



Snout length: in front of orbits 7.2, 9.8; in front of mouth 10.3, 12.6. 



Orbits: horizontal diameter 4.8, 5.0; distance between 9.8, 10.2. 



Spiracles: length ^.^, 5.4; distance between 12.6, 12.6. 



Mouth: breadth 8.3, 8.3. 



Exposed nostrils: distance between inner ends 6.5, 7.0. 



Gill openings: lengths, ist 1.8, 1.8; 3rd 2.1, 2.1; 5th 1.2, 1.2; distance between 

 inner ends, ist 13.7, 14-5; 5th 7.8, 6.7. 



Dorsal fin: vertical height 3.1, 3.0; length of base 6.1, 6.2. 



P^/wVj; outer margin 11.5, 13.2. 



Distance: from tip of snout to center of cloaca 53.8, 57.8 ; from center of cloaca 

 to origin of tail spine 18.8, 20.3; to tip of tail 124.0, iii.o. 



Disc lozenge-shaped, its extreme breadth 1.6— 1.8 times as great as length from 

 tip of subrostral fin to rear limits of pectorals; anterior margins nearly straight or weakly 

 convex; posterior margins weakly and uniformly concave; outer corners considerably 

 narrower than in M. goodei (cf. Fig. 102 with 104); posterior corners an abrupt angle 

 of about 80°; inner margins weakly convex, about as long as breadth of mouth. Axis of 

 greatest breadth about 70 "/o of distance from tip of subrostral fin back toward axils of 

 pectorals. Breadth between axils of pectorals less than distance between inner ends of 

 first gill openings by a distance ^U-^l2 as great as that between exposed nostrils. Tail 

 moderately stout anterior to spine, tapering thence rearward to whiplash tip; its length 

 from center of cloaca as much as 2.3—2.5 times as great as length of disc to tip of rostral 

 fin in small specimens, somewhat shorter relatively in large ones; usually more or less 

 damaged. 2* 



One or two tail spines, the anterior one the smaller (when there are two), hence 

 evidently the more recently formed; the largest, when fully developed, about as long as 

 distance between eyes; about o. i as broad where exposed at base as long; origin of 



24. Subrostral fin, anterior to front of cranium, 0.9-1.2 times as long as distance between outer ends of nostrils in M. 

 fremininllii; 0.7-1.0 times that long in female M. goodei. 



25. Garman, Proc. U. S. nat. Mus., 8, 1885: 39; Jordan and Evermann, Bull. U. S. nat. Mus., 47 {3), 1898: 2755. 



26. In one specimen, 600 mm wide, from Woods Hole, the tail had been lost posterior to the spine and the wound was 

 entirely healed over. 



