152 CEYLON PEARL OYSTER REPORT. 



segment two and a half times as long as the distal (figs. 1, 11). Abdomen of male 

 with the 8th segment slightly asymmetrical (figs. L3, 14, 15), the "horns" being both 

 inclined towards the left, so that while the right horn is closely applied to the 9th 

 segment, the left is somewhat divergent from the axis of the body ; both horns are 

 falcate at the tip. 



Habitat: Coasts of Ceylon. Old Dutch Modragam Paar, numerous males and 

 females ; Galle Bay, two males and one female ; off Mutwal Island, Gulf of Manaar, 

 two females ; off Manaar Island, several young specimens. 



This species is most nearly allied to H. fiaviventris, Eschs., of all members of the 

 genus hitherto described. It differs from that species principally in the shape and in 

 the slight asymmetry of the "horns" of the 8th abdominal segment of the male. 

 The form of this segment in the present insect shows an interesting stage of transition 

 between the symmetrical condition found in the great majority of the species of 

 Halobates and the excessive irregularity of H. micans, Eschs. (H. wullerstorjfi , 

 Feauenf.), in which the left horn of the segment projects almost at right angles to 

 the axis of the body. 



In colour H. herdmani resembles the other species of the genus. The dorsal 

 and lateral surfaces appear deep blue-black when wet, and ashy grey (owing to the 

 dense pubescence) when dry. On the head are the usual pair of orange triangular 

 marks, while the feelers and legs are black. The thoracic sternum is dark centrally, 

 showing only two pale elongate patches towards the lateral sutures (fig. 14) close to 

 the bases of the hind legs. The abdominal sterna are mostly pale, but they appear 

 dark laterally and along their hinder borders ; the 1st abdominal segment, on which 

 is the opening of the repugnatorial glands, is deep brown. 



The sutures, partially marking the junctions of the anterior abdominal terga, can 

 be unusually well seen in this species (figs. 1, 2), and the male has a median longi- 

 tudinal suture extending from the front of the mesothorax to the hinder edge of the 

 2nd abdominal segment. The recognition of the transverse dorsal sutures reminds 

 us that though the abdomen is indeed much reduced in this genus, as compared with 

 most of its fresh-water allies, yet the peculiar modification of the body is principally 

 due to the abnormal extension of the mesothorax, and to the backward growth of 

 that segment and of the metathorax on either side of the anterior abdominal 

 segments. 



Fore Legs. The fore legs of the various species of Halobates have been 

 frequently described and figured, affording as they do excellent diagnostic characters. 

 A few details are, however, worthy of especial notice. The tarsal segments in the 

 present species are longer and more slender in the female (fig. 9) than in the male 

 (figs. 5, 6). The whole of the limb is covered with a fine pubescence, but on the 

 upper surface a number of short, stout sj>ines are interspersed among the delicate hairs 

 (fig. 5), these spines being especially strong in the male and being absent from the 

 under surface of the foot in both sexes (figs. f>, 9). At the end of the shin, however, 



