56 DR J. H. ASHWORTH 



the anteroposterior diameters of the valves of the protegulum* and probably also 

 the form of the chsetse. These features may therefore be found useful in the deter- 

 mination of the species of larvae, but a definite decision as to their taxonomic value 

 can only be reached after they have been examined in further series of specimens. 



Judging from the large size attained by the oldest examples, the larvae found in 

 the southern portion of the Red Sea developed under very suitable conditions. It 

 will be observed that these larvae form a regular series, there being no aberrant 

 members, and they probably afford a fairly reliable criterion of the normal course of 

 development in a favourable environment. 



Breeding Seasons. 



Dr Yatsu states that the breeding season at Misaki is very short, and is certainly 

 restricted to a month and a half of the summer — from the middle of July to the end 

 of August. He estimates that the period which elapses from the onset of develop- 

 ment to the stage with 15 pairs of cirri is about six weeks. Assuming that my 

 larvae had developed at about the same rate, the oldest specimen, with 15 pairs 

 of cirri, taken on June 21, 1914, in the southern portion of the Red Sea, would be 

 one of the products of a spawning which had taken place in the first half of May. 

 Spawning evidently continued until, or was resumed about, the end of May, for a 

 much younger larva, only half as long as the preceding, was taken at the same time 

 and place. The finding of two large larvae, with 14 and 15 pairs of cirri respec- 

 tively, in the southern portion of the Red Sea on October 22, is evidence that a 

 spawning occurred in the first half of September. The specimen in Dr Annandale's 

 material was taken on March 25, 1901, in the Strait of Bab-el-Mandeb, and probably 

 had developed from an egg fertilised about a month previously. The evidence 

 available in regard to the southern end of the Red Sea indicates that there is a 

 succession of spawnings extending at least over the period from the beginning of 

 March to the early part of September. 



Captain Sewell records the occurrence of larvae during the winter months, 

 December and February, in the plankton off the south coast of Burma. I found one 

 young larva, which was probably from two to three weeks old, in the Indian Ocean, 

 about 3° N. lat., and 80° E. long., on October 14, 1914. 



Comparison of the Larv.e of Lingula anatina with Brooks's Larv.e of 



Glottidia audebarti. 



As Brooks's memoir (1879) on the development of Glottidiais not easily accessible, 

 a few notes on his specimens are given here, and their characters compared with 

 those of the available examples of Lingula anatina. 



* The primary shell is laid down while the larva is enveloped by the egg-membrane, and hence the protegula 

 and the hinge-line are determined under relatively uniform conditions ; later the larva is subject to more diverse 

 conditions, which cannot but react upon such characters as the secondary shell and the peduncle. 



