ON LARViE OF LINGULA AND PELAGODISCUS (DISCINISCA). 47 



those of known parentage, though it is nearer to that of Lingula anatina, and 

 should probably be referred to this genus. I am not aware of a record of adult 

 specimens of any species of Lingula from the west coast of Africa, so that no clue 

 to the species of Professor Simroth's larva can be obtained. 



The Larvae of Lingula anatina. 

 Localities. 



The localities at which the larvae were obtained may. be stated thus : — 



(i) Southern portion of the Red Sea, about lat. 15° N., long. 42° E. ; June 21, 

 1914 ; depth of water about 16 to 40 fathoms ; fourteen larvae. 



(ii) Indian Ocean, about lat, 3° N., long. 80° E. ; October 14, 1914 ; depth of 

 water about 2200 fathoms; one larva. The noteworthy feature about the record 

 from this locality is the great depth of water in and all round the area where the 

 larva was obtained, the nearest shallow water being that on the coast of Ceylon, 

 distaut some 200 miles north. Lingula is generally found between tide-marks or 

 in shallow water. 



(iii) Southern portion of the Red Sea, near the edge of the Dahalak Bank in 

 lat. about 16° N. ; October 22, 1914; depth of water about 30 fathoms, but there 

 were shallow areas of about 7-9 fathoms within a few miles ; two larvae. 



So far as I am aware, Lingula has not been recorded from the Red Sea, and the 

 only recorded examples from the Indian Ocean are from the coast of Burma. Dr 

 Annandale tells me that he has seen Lingula in abundance on the islands off the 

 Siamese state of Trang, on the west coast of the Malay Peninsula, and that there are 

 specimens in the Indian Museum, Calcutta, from the Andaman Islands and the 

 coast of Burma. 



Description of the Larvse (Plate IV). 



It is not proposed to give a detailed description of the larvae, as they agree in 

 general with the excellent account given by Dr Yatsu, but attention will be drawn 

 to their principal features, and to certain points in which my larvae differ from those 

 studied by previous observers. 



The specimens may be divided into five groups, according to the number of their 

 cirri, which is probably the most reliable indication of the age of the larvae. 



(i) Larvse with 8-10 pairs of cirri. — The youngest stage obtained was taken 

 in the Indian Ocean (locality (ii)), about 4° nearly due south of Colombo. The 

 shell-valves are "52 mm. long and "62 mm. broad, and have the form shown in 

 figs. 1, 2. The straight hinge-line* is "3 mm. long, and the distance between the 



* The cuticular shell first formed over the dorsal and ventral mantle-folds of the larva is circular in outline 

 (Yatsd) ; a large fold is formed posteriorly which divides the shell into dorsal and ventral valves or protegula 

 (Beecher). The valves increase in thickness, and later, as the secondary shell is added, in size ; but the fold, as it is no 

 longer in contact with the mantle, remains a mere film of cuticle, which, however, serves for some time as a hinge 



