line. The distal end is produced into two short pointed pieces. The second single piece underlies or is telescopically pushed into the first and is of the same or very similar form as the first. Connected with the female genital apparatus were paired internal tubular appendages first correctly recognized in E. fischeri. These are also well seen in specimens of E. remipes [pl. 8, fig. 1] and E. lacustris [pl. 12, fig. 2]. In one of the representatives of the latter species [Buffalo Society of Natural Sciences] both tubes lie to one side of the median lobe [see text fig. 20] thereby indicating that they extended free into the interior of the body.
In the male the two lateral opercular plates are more regularly rectangular in outline and come into contact along the median line. The genital appendage is very small and composed only of two single pieces. No pentagonal areas are set off by sutures. The principal single appendage consists of a median piece with parallel sides exposed to the outside and two larger wings underlying the opercular plates; the second appendage is very small, triangular and adjoins the first.
In other genera, as Hughmilleria and Pterygotus, the genital appendages are clearly much simpler. In Hughmilleria only one sagittate-based lobe is found on the female operculum [pl. 62, fig. 9, 10] and in the male a convex, broadly lanceolate lobe [pl. 62, fig. 11].
In Pterygotus these sexual appendages are not yet clearly distinguished, but they seem to be little advanced beyond those of Hughmilleria. The female appendage in its simplest form [P. bilobus, see Woodward, 1869, p. 61, pl. 12, fig. 1C; Laurie, 1893, pl. 2, fig. 14] is a straight, narrow, very slightly expanding plate with a ridge down the middle and ending in a bluntly triangular point, while, where more highly developed, as in P. osiliensis, it possesses a rhombic sagittate base, connected by sutures with the lateral opercular plates, and continued into the free club-shaped principal part with rounded extremity. In some cases, as in P. anglicus, [see Huxley and Salter, pl. 3] and in an unidentified form from Otisville [pl. 78, fig. 3] the extremity was expanded into a disklike body, the whole appendage
