44 Mr. J. W. Salter on the occmrence of a Fish inent of the rectum. Hepatic organ the same. Organs of ge-neration double, occupying the middle part of the body; their form undetermined. Ocelli at some distance from the head, of the same colour as in U. infrequens. Size. l-7th of an inch long and 1 -600th of an inch broad. Male. The same as the female, but with a large, thick, curved tail, obtuse at the extremity, tuberculated in its inner curvature, and furnished on each side with a row of short setse extending from above the anus towards the tip ; also three or four setae on the outer curvature. Testis and penis the same as in the fore-going species ; form of the testis undetermined. Hab. Same. Loc, Island of Bombay. Urolabes parasitica^ n. sp. Female, Linear, cylindrical, unstriated, gradually diminishing towards the head, which is obtuse and without papillae, and also towards the tail, which is long and conical. Mouth and anus as in the foregoing species. Vulva a little in front of the middle of the body. Alimentary canal and hepatic organ the same. (Esophagus commencing in an expanded oral orifice, immediately becoming narrowed into a straight uniform tube ; naked at the commence-ment, but soon surrounded by a sheath, which goes on increasing in width to the point of union of the oesophagus and intestine, after which it continues of uniform calibre to the termination of the latter. Organs of generation double, occupying the middle third of the body, their form undetermined ; filled with ova diminishing in size with their distance from the vulva, and all presenting the germinal vesicle. Size. l-43rd of an inch long. Male. Unseen. Hab. Peritoneal cavity of Nais albida, in more or less abun-dance during the " rains," when this Nais makes its appearance in the Glceocapsa mentioned. Loc, Island of Bombay *. [To be continued.] IV. — On the occurrence of a Fish (Pteraspis) in the Lower Ludlow Rock. By J. W. Salter, F.G.S. The discovery of a true Fish in beds of the Silurian system considerably older than the famous " bone-bed " of the Upper Ludlow rocks is a fact of much interest. It is desirable at once * For a small figure of this worm, see 'Annals,' scries 3, vol. ii. pi. 4. fig. 50.
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