When trawling with a small beam trawl on July 9th last, a couple of miles north of the Eddystone, I obtained a large number of specimens of a fish which was quite unfamiliar to me. I found it was Crystallagobius Nilssonii. The chief characters distinguishing the species are the presence of only two rays in the anterior dorsal fin of the male, and the almost complete absence of this fin and of the pelvic fins in the female. The adult male is 4.4 cm. long, the female about 3 cm. When alive the fish is very translucent, and it is entirely destitute of scales. The species was first described by Düben and Koren in 1844 from half a dozen specimens taken near Bergen. Robert Collett has well described it in the Proceedings of the Zoological Society for 1878, having taken twenty-eight specimens at about 30 fathoms in the Christiania Fjord in the years 1875—1877. Only forty-five specimens altogether had been taken off the south and west coast of Norway at the time when Collett wrote. I captured 201 specimens in a single haul of the trawl, 188 of which were female and 13 male. Nearly all were adult, the eggs being visible through the integuments in the female. A few not quite full grown are included among the 188 reckoned as female, and some of these may prove on closer examination to be young males. In any case the excess of females is very great.