Before 1888 no specimen of Tornaria, the well-known pelagic larva of Balanoglossus, had been taken off the English Coast. But on August 9th of the past year Mr. Weldon, using the surface net near the Eddystone Lighthouse, took several young specimens of Tornaria, and subsequently the same gentleman, during a cruise of a week's duration towards the end of August, captured many larger and more mature specimens of the same larva. Other specimens were taken by us up to September 21st, and in the month of August, Mr. Rupert Vallentin found several specimens in the vicinity of Falmouth.The specimens taken on these occasions form the subject of the present memoir, and their anatomy is detailed at some length, both because of the interest attached to a form bitherto unknown to England, and because it is in some respects of morphological importance.The specimens taken by us came from the offing, and were not taken within four miles of theshore; Mr. Vallentin's Tornaria were found close to the shore at Falmouth. As he was able to bring his back alive and preserve them at leisure in his laboratory, they are better preserved than those taken by us, since we were obliged to preserve our catch in a somewhatrough manner out at sea. An examination of Mr. Vallentin's specimens leaves me no doubt that the larva is Tornaria Kröohnii, aspecies found in the Mediterranean. The different forms of Tornariahave not been with certainty referred to their adult forms, but T. Kröohnii must belong to one of the Mediterranean species of Balanoglossus, that is to say, to B. Kowalevsltii, B. minutus, or B. claviger, species which have not hitherto been recorded from the English Channel, unless we suppose that the larva of B. salmoneus v. sarniensis, which occurs in the Channel Islands andat Roscoff, is identical with Tornaria Kröohnii.