Mr. R. T. Pocock on the Genus Urodacus. 169 



EXPLANATION OF PLATE IX. 



Fig. 1. Difflttgin urccolata, Carter, engaged in division and shell -formation. 



The new shell composed of fragments of glass. 

 Fig. 2. The same, with half the shell removed. In the endoplasm besides 



sand-grains there are a number of red nuclei (here black). 

 Figs. 3 a, b, c. Shells of Difflugia urceolata divided in various directions 



indicated by the dotted lines. 

 Fig. 4. Polystomella crispa, Linn. The youngest chambers have been 



removed and a new calcareous wall has beim formed over the 



lesion. 

 Fig. 5. The same, showing the regeneration on a largo scale, a, from 



the side ; b, from in front. 

 Fig. 6. The same, with six chambers partially removed, and with a 



common calcareous layer deposited over the cut surface. 



XX. — The Species of the Oenus Urodacus contained in the 

 Collection of the British {Natural-History) Museum, liy 

 R. I. Pocock, Assistant, Natural-History Museum. 



[Plate VIII.] 



This genus was described by Peters in 1861. It differs from 

 other Scorpions, which are characterized by the possession of 

 a pentagonal sternum and two lateral eyes, by the presence of 

 a median keel upon the lower surface of each of the caudal 

 segments. 



Urodacus novcB-hoUandice^ the type of the genus and 

 hitherto its sole representative, was described by Peters 

 (Monatsber. d. k. Akad. Wissen. Berlin, 1861, p. 511) from 

 specimens obtained from West Australia ; and Count Keyser- 

 ling, in his work ' Die Arachniden Australiens,' p. 34, has 

 published a lengthy description of it, the description and 

 accompanying figure (PI. VIII. figs. 1, 1 a) being taken from 

 specimens also from West Australia. 



Whilst examining for identification the Scorpions contained 

 in the collection of the British (Natural-History) Museum, I 

 found that this genus Urodacus is represented by no less than 

 four well-marked species. Three of these I believe to be new 

 to science, and have consequently described ; the fourth I 

 refer to U. novcB-hollandice of Peters. 



Of this last-named form the Museum possesses eleven speci- 

 mens, a series which presents some interesting and, I believe^ 

 new facts connected with the sexual variation and the geogra- 

 phical distribution of the species. 



