58 DR J. H. ASHWORTH 



THE LARVAE OF PELAGODISCUS (DISCINISCA). 



Previous Records of the Larvae of Discinid^e. 



(a) Larvae of Pelagodiscus (Discinisca ) atlanticus (King). — Fritz Muller 

 (1860, 1861) was the first to describe a larva of an ecardinate Brachiopod. He 

 recognised that his larvae were those of some Brachiopod, but in his published 

 accounts did not refer them to any genus, though he evidently not long afterwards * 

 reached the conclusion that they belonged to the genus Discina.^ He probably saw 

 about a dozen living larvae, which he collected in the years 1859 and 1860 near 

 Desterro on the southern portion of the coast-line of Brazil. 



The only other observer who has hitherto seen a living larva is Dr Yatsu (1902, 

 p. 105) who found, in the plankton near Misaki (Japan), a specimen which is 

 probably referable to the species P. atlanticus. 



Professor Blochmann (1898) studied ten preserved examples taken in the 

 plankton off the island of Bintang, about 45 miles south-east of Singapore. 



(b) Larvae of other Discinidae. — Muller obtained another larval form of a species 

 of Discina, which he stated, in a letter to Professor Morse,* belonged to the species 

 D. radiata Dunker, but I am unable to find any further reference to this larva, no 

 description of which seems to have been published. 



Professor Simroth (1897, pp. 3-6) has described two larvae obtained by the 

 Plankton Expedition. The smaller one, from Palmas roadstead, has a transverse 

 diameter of "22 mm., and only 3 pairs of cirri. It is further remarkable for 

 possessing on each side four very long chaetae. The larger larva, taken in lat. 

 5° 9' N., and long. 20° 3' W., at a depth of 1000-1200 metres, has a transverse 

 diameter of '42 mm. This larva has 4 pairs of cirri, which are much more slender 

 and elongate than those of P. atlanticus, and the median tentacle is also elongate 

 and terminates in a bulbous dilatation. There are only two chaetae on each side, 

 which appear to be equal in length and simple. Both these larvae are .referred by 

 Professor Simroth to the genus Discina. 



Eichler (1911) has given a short account of two larvae obtained by the German 

 South Polar Expedition near the winter station of the Gauss (lat. 66° S., long. 

 90° E.), from a depth of 3000 metres. The specimens were 787 and *825 mm. 

 respectively in transverse diameter, and had 4 pairs of slender cirri of unusual 

 length. On each side there were four stronger chaetae, all of similar form and 



* Professor Morse (1873, pp. 356, 357) states that he received " a letter from Herr Muller, accompanied with a 

 sketch of another larval form of Discina, in which he describes features similar to those above mentioned [referring 

 to his abstract of the account of Muller's larva? from Uesterro], and states that the species has been denned by 

 Professor Dunker as I), radiata." By the courtesy of Mr E. A. Smith I have been able to see Dunker's description 

 of D. radiata (Malak. Blatt., vol. viii, p. 39, 1861) : there is no reference to the larva. 



t The genus Discina was subdivided by Dall in 1871 into Discina (sensu stride-) and Discinisca, and the latter 

 was again divided by Dall in 1908 into Discinisca (s. str.) and Pelagodiscus. Discina atlantica King falls into the 

 last-named section, and its correct designation is therefore Pelagodiscus atlanticus (King). 



