164 Memoirs of the Indian Museum. [Vol. IV, 



wholly absent , and the submedian ridges in the middle of the dorsal surface are 

 strongly convergent posteriorly. 



The only known specimen, a female 56 mm. in length, is recorded by de Man from 

 the Mergui Archipelago. Patience has examined an example from the same locality, 

 which in the form of the rostrum resembles the type of this species, while the telson 

 shows the characters of chiragra (form acutus) . 



3. Gonodactylus demani/ Henderson. 

 Plate IX, figs. 108-111. 

 1887. Gonodactylus, n. sp., de Man, Arch. f. Naturgesch., LIU, i, p. 574, pi. xxii a, fig. 7. 

 1893.' 2 Gonodactylus Demanii, Henderson, Trans. Linn. Soc. Zool. (2), V, p. 455, pi. xl, figs. 23, 24. 

 1905. Gonodactylus Demani, Nobili, Boll. Mus. Torino, XX, no. 506, p. 11. 



1905. Gonodactylus spinosus, Lenz, Abhandl. Senck. naturf. Ges. Frankfürt, XXVII, p. 387, pi. xlvii, 



fig. 12. 



1906. Gonodactylus De Mani, Nobili, Ann. Sei. Nat. Zool. (9), IV, p. 330. 



1906. Gonodactylus de Mani, Nobili, Bull. Sei. France et Belg., XL, p. 158- 



1907. Gonodactylus demani, Borradaile, Trans. Linn. Soc. Zool. (2), XII, pp. 210, 212. 

 1910. Gonodactylus De Mani, Lenz, in Voeltzkow 's Reise in Ost- Afrika, II, p. 572. 



This species is very closely allied to G. chiragra and appears to be distinguished 

 from it only by the following characters : — 



1. The dorsal processes of the ophthalmic somite are (fig. 108) extremely small and 



inconspicuous and take the form of two very small transverse plates with 

 straight or almost straight anterior edges. 



2. The telson (figs. 109-111) has three swollen ridges in the middle of its dorsal 



surface as in G . chiragra, but the median one is very strongly convex in 

 lateral view and its depth, measured from the summit to a point vertically 

 below on the inferior surface is equal to half its extreme breadth. The three 

 median ridges and those running to the apices of the submedian and inter- 

 mediate marginal spines occupy practically the whole surface of the telson 

 and are separated from one another merely by narrow V-shaped furrows ; the 

 interspaces found in G. chiragra are absent. This feature is well shown on 

 the submedian spines ; the latter are evenly convex from side to side from 

 the apex to the base and never bear a median keel distinct from the general 

 surface as in G . chiragra. The telson, in all known specimens except one (var. 

 espinosus) is beset with tubercles or spinules that vary greatly in size and 

 number. 

 In the typical form of G. demani the telson is broader than long, the intermediate 

 marginal teeth are well-developed and the lateral teeth, though small, are usually 

 quite distinct. The figures on pi. IX (figs. 109-111) will give some idea of the range 

 of variation in the number and size of the spinules. Inmost examples they are absent 



1 See addendum, p. 198. 



% Henderson's G. demani has one month's priority over G spinosus, Bigelow; the latter is here re- 

 garded as a variety of the former. 



