ON DIRECT DEVELOPMENT IN A DROMIID CRAB. ] 93 



10. Direct Development in a Dromiid Crab. 

 By Stephen K. Montgomery, B.A., B.Sc* 



[Received February 10, 1922 ; Read March 7, 1922.] 

 (Text-figures 1-3.,) 



The specimen here described is in the collection of the British 

 Museum (ISTatural History), and was submitted to me for 

 examination by the the kindness of Dr. W. T. Cahnan, to whom 

 thanks are also due for much assistance in studying it. The 

 specimen was presented to the Museum many years ago by the 

 late Dr. Henry Woodward. It is dried, and the only information 

 regarding its origin is the locality, "Bass's Strait," given on the 

 label. 



The specimen is an adult female Petalomera lateralis (Gray)t, 

 a species referred to by Haswell + as " very common " in Australian 

 seas. 



Under the abdomen are carried about 20 young in a post-larval 

 stage, which, although possessing the same general form as the 

 adult, differs from it in many details. 



A similar occurrence is recorded by Miss Rathbun § in a paper 

 to this Society in the case of the Oxyrhynch Naxioides serpid'ifera 

 (Guerin) ; this is the only other available record of such a case 

 among marine Brachyura. 



The adult agrees entirely with the descriptions, and the figure 

 of Stimpson ||. It is figured here for comparison Vvdth the young. 



Only one stage of development has been observed in this case, 

 not two as in the case of iV. serpulifera. 



The carapace of the young crab is longer than broad, the 

 measurements being about 1-5 mm. long and 1"2 mm. br-oad, is 

 flatly convex, much flatter than in the adult, and in the centre 

 shows, under a high magnification, a minute reticulation. The 

 regions are well marked, again in contrast to the adult, and there 

 are numerous veiy fine hair-like spines on the upper surface. 



The front consists of three very prominent forwardly directed 

 spines, each of which bears 5 to 8 pointed spinelets. The middle 

 spine is directed forward and downward and, with the two 

 lateral spines, forms a deep, almost V-shaped gutter between 

 the supra-orbital borders, the opening of the Y pointing forwards 

 (text-fig. 1). 



The supra-orbital border bears a similar prominent spine with 

 accessory spinelets, which is directed forward and outward 

 (text-fig. 1, a). Behind this spine the border runs almost directly 

 backwards ; there is a slight protuberance bearing a few spinelets 



* Communicated by Dr. W. T. Calman, F.R.S., F.Z.S. 



t For the transference of this species from Cryptodromia io Petalomera, cf. L. A. 

 Borradaile, Ann. Maa-. Nat. Hist. (7) xi. 1903, p. 3u0. 

 X W. A. Haswell, Catalo2;ue of Aust. Stalk- and Sessile-eyed Crustacea, 18S2, p. 139. 

 § Marv J. Rathbun, Pro^c. Zool. Soc. 1914, p. 653, pi. ii. figs. 9, 10. 

 II W. Stimpson, Smithsonian Misc. Coll. 1907, xiix. pi. xx. fig. 3. 



Proc. Zool. Soc— 1922, No. XIII. 13 



