2 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 123 



Lanchester attempted to arrange these in transitional sequences 

 leading to a typical form ; several of his transitional forms were based 

 on small specimens (G. c. var. incipiens, G. c. var. segregatus) with 

 obviously adult features of telson morphology. Kemp noted that 

 small specimens varied more than adults and proposed (1913, p. 151) 

 three hypotheses to explain observed variation in Indo-West Pacific 

 species of the genus: (1) small specimens exhibiting wide variation 

 die before reaching maturity; (2) small specimens represent dwarf 

 races capable of "breeding and perpetuating their precise type"; 

 (3) with growth, small specimens lose their characteristic features 

 and assume the typical facies. Kemp suggested that the second 

 hypothesis was improbable and that most likely variation could be 

 explained by growth changes. 



More recently, students of the group have begun to accept the 

 possibility that species might mature at different sizes. Bigelow (1931) 

 suggested some support for this hypothesis, and Serene (1954) recog- 

 nized two dwarf races ("race naine") from Viet Nam: G. chiragra var. 

 viridis and G.falcatus var. ternatensis de Man, 1902. In the western 

 Atlantic, Manning (1967) reported on small species of Gonodactyhts 

 that had adult features at TL 20 mm and that could be distinguished 

 with no difficulty from the larger species. 



The current study shows that in addition to G. demanii there are 

 six recognizable species of small size in the Indo-West Pacific, and a 

 survey of the literature indicates that several more may have been 

 recognized in the past by other authors. These include G. chiragra var. 

 affinis de Man, 1902, and G. c. var. conjinis de Man, 1902, both from 

 Ternate, Indonesia, and G. c. var. segregatus Lanchester, 1903, from 

 the Maldive and Laccadive Islands. Gonodactylus affinis and G. 

 segregatus are, from their accounts, very similar, and G. conjinis may 

 prove to be conspecific with G. incipiens, recognized below. 



One of the features characteristic of G. demanii, sensu stricto, and 

 G. hendersoni, new species, described herein, is the absence of setae 

 on the inner edges of the uropodal exopod and endopod; G. demanii 

 may have a few proximal setae on the inner margin of the endopod, 

 but most of the inner margin is bare and smooth. In this feature 

 these two species resemble two other species currently placed in 

 Mesacturus Miers (= Gonodactylus Group II of Kemp, 1913), M. 

 drepanophorus (de Man, 1902) and M. herdmani (Tattersall, 1906). 

 The telson morphology of these two pairs of species also seems to 

 be similar, but the two species placed in Mesacturus differ in having 

 a sharply trispinous rostral plate. Further study may show that 

 both M. drepanophorus and M. herdmani should be reassigned to 

 Gonodactylus, for neither have the strong^ recurved spines on the 

 uropodal exopod characteristic of the other species of Mesacturus. 



