178 Memoir Sears Foundation for Marine Research 



usually less than 54, in the upper jaw, while R. ocellata always has at least 72 series 

 and usually more than 80. i" In the case of sexually mature males, size is an equally 

 dependable specific character, for R. erinacea grows only to a length of about 2 i inches, 

 whereas R. ocellata does not mature sexually until it has reached a length of at least 

 26—28 inches. Adults of R. erinacea resemble those of R.fyllae of West Greenland 

 and the northeastern Atlantic in arrangement of thorns, in proportional dimensions, 

 in the shape of snout, and in the fact that the two dorsals are confluent. But they are 

 easily distinguishable from R.fyllae by their shorter tails and by the fact that the upper 

 surface of R. erinacea between the thorns is smooth (partly spinulose in R.fyllae') and 

 the margin of the disc less deeply concave opposite the spiracles. There is no dangre 

 of confusing young specimens of the two; in R.fyllae the upper surface is uniformly 

 prickly with the large thorns on the disc limited to the midline of the back, to the 

 shoulders and to the head, whereas in the young of R. erinacea the disc as a whole is 

 thorny with the skin smooth between the thorns. Neither R. erinacea., R. ocellata, nor 

 R.fyllae is likely to be confused with any other Skate of the western North Atlantic, 

 so characteristic are the thorn pattern, shape of disc, and proportionate dimensions 

 of each. 



R. erinacea falls closest to R. naevus Miiller and Henle 1841 among European 

 Skates in shape of disc, relative length of tail, distribution of thorns, and number of 

 teeth; also, in the fact that the mid-dorsal row of thorns is lost with growth. However, 

 the midbelt of the disc and the anterior part of the tail are thornier in R. erinacea than 

 in R. naevus, whereas the upper surface of the disc is prickly generally between the 

 thorns on R. naevus but naked between them on R. erinacea. The inner part of each 

 pectoral, which is marked ordinarily with a conspicuous ocellar spot in R. naevus, 

 is not so marked in R. erinacea. R. erinacea does not closely resemble any Skate known 

 from the South Atlantic or from the Pacific Coast of America. 



Description. Proportional dimensions in per cent of total length. Male, 441 mm, 

 and female, 449 mm, from Massachusetts (Harv. Mus. Comp. Zool., Nos. 547 and 

 708 respectively). 



Disc: extreme breadth 57.2, 57.7; length 46.5, 46.0. 



Snout length: in front of orbits 9.9, 10.2; in front of mouth 9.5, i 1.3. 



Orbits: horizontal diameter 2,-^^ 3-8; distance between 4.8, 4.9. 



Spiracles: length 2.9, 2.9; distance between 6.8, 6.9. 



Mouth: breadth 8.0, 8.2. 



Nostrils: distance between inner ends 6.8, 6.2. 



Gill openings :\tr\gXh?,, ist 1.7, 1.8; 3rd 2.0, 1.9; 5th 1.6, 1.6; distance between 

 inner ends, ist 14. i, 15. i; 5th 7.3, 8.9. 



First dorsal fin: vertical height 2.8, 3.1; length of base 6.6, 6.7. 



Second dorsal fin: vertical height 2.5, 2.9; length of base 5.9, 6.2. 



Pelvics: anterior margin 13.6, 11.6. 



Distance: from tip of snout to center of cloaca 44.3, 45.4; from center of cloaca 



118. See p. 242, footnote 74. 



