92 PROCEEDINGS OF THE ACADEMY OF [1879. 



rasp-sheath very obliquely descending between the muscular 

 masses of the tongue, and appearing on the lowest part of the 

 back side of the bulbus pharyngeus (fig. 10c). The rachis (fig. 

 96) with nineteen rows of teeth on the anterior 'margin, and with 

 one on the superior; besides three loose median teeth laying in 

 the pocket on the inferior end of the tongue ; in the sheath twenty- 

 two developed rows and two- undeveloped, the total number of 

 rows was thus forty-four. The color of the median teeth horn- 

 yellow, that of the lateral much brighter yellowish; the breadth of 

 the eldest median teeth about 0.16 mm., of the eighth about 0.18, 

 and of the latest developed 0.20 mm. The form of the teeth ex- 

 actly as in the D. arborescens (cf. PL II. fig. 14). The median 

 ones (fig. 8-10) with a very fine denticulation on the margin, much 

 finer than in the typical species, and not reaching so far (cf. PI. II. 

 fig. 14, and PI. III. fig. 10) out toward the point. The lateral plates 

 number also about fourteen, of typical form ; the first sometimes 

 with traces of a slight serrulation on the inside of the hook, the 

 following mostly with about five to six (sometimes even seven to 

 nine) sharp denticles on the outside (fig. 11); in the three to four 

 (rarely five) external plates the free hook disappearing more and 

 more together with the denticles ; the outermost, or the two outer- 

 most, were very thin 1 (PI. III. fig. 5). Variations in the form of the 

 lateral teeth, and coalescence of two teeth were often observed, 

 quite as in the typical species (cf. PI. III. fig. la). 



1 According to Alder and Hancock (1. c.) the number of rows of teeth in 

 the D. arborescens is about forty, with nine lateral teeth on each side. 

 Meyer and Moebius mention (1. c. p. 44) a " Radnla," with forty-four rows 

 (by which is probably meant the total number of rows on the rhachis and 

 in the sheath), and with ten lateral teeth, and the same number of lateral 

 teeth has been indicated by Loven. In my former examination (of two 

 individuals) I saw sixteen to twenty -two rows on the rhachis and twenty- 

 five to twenty-seven in the sheath, or a total number of forty-one to forty- 

 nine rows, with ten to thirteen lateral teeth. In my present examination 

 of five specimens of D. arborescens (like the former, all from the Greenland 

 coast at Jacobshavn, etc. ) I find the number of rows on the rhachis varying 

 in small individuals from thirteen to eighteen, and those in the sheath from 

 sixteen to twenty-three, the total number thus varying between twenty -nine 

 and forty-one ; in three large individuals, having a length of 35.0 mm., the 

 number was 13 + 20 (33), 16 + 20 (36), and 22 + 26 (48) ; the number of 

 lateral teeth being eleven in the former and thirteen in the latter. In all 

 specimens two or three median teeth were found loose at the under side of 

 the root of the tongue. 



