360 C. FORSTER COOPER. 



3. Heteropleuron cinghaleiise Kirkaldy. Coast of Ceylon. 



4. H. maldivense, n. sp. Maldive Islands and Zanzibar. 



5. Dolichorhynchus indicus Willey. " Black Pagoda," off the Orissa coast of India. 



6. Branchiostomum pelagicum Gunther. One specimen each from Indian and Pacific 

 Oceans. 



DESCRIPTION OF PLATE XVIII. 



Fig. 1. Asymmetron lucayanum. 



Fig. 2. Heteropleuron maldivense. 



Fig. 3. Larva with 60 myotomes and 16 gill slits (length 5'75 mm.). 



Fig. 4. An older larva with 61 myotomes and 31 gill slits (length 6'5 mm.). 



Fig. 5. A ventral view of the above larva shewing the extent of gill slits in the ventral surface. 

 The slits are seen to be of a roughly rectangular shape, the outlines being somewhat obscured 

 by the twisting of the edges. 



Fig. 6. Enlarged view of the head of Fig. 3. e. eye spot, b. brain, p.p. preoral pit, p.s.o. pre- 

 oral sense organ, end. endostyle, c.s.g. club-shaped gland, g.s.\. first gill-slit. 



