1907.] CRUSTACEA OP THE THIRD TANGANYIKA EXPEDITION. 



261 



nearly to the forms P. hilgenclorfi (Pfefier) and P. johnstoni 

 (Miers). In order to render a comparison more easy, the 

 diverging characters of these thi'ee species are given in tabular 

 form, while it may hei'e be stated that P. orbitospijius is a speciey 

 certainly moi-e easily recognised than some of those which are 

 allied to it. 



Mlgendorji (Pfeff.) 

 (not liilgendorfi Hilg.). 



orhitospiHus, sp. ii. 



Johnstoni (Miers). 



Carapace somewhat flat- Carapace coiisiderablj' 

 teiied. flattened. 



Carapace somewhat flat- 

 tened. 



Antero-lateral margins | Antero-lateral margins Antero-lateral margins 

 granulated. denticulated. granulated. 



External orbital angle 

 rather acute. 



Pronto-orbital width "71 

 that of carapace. 



External orbital angle pro- External orbital angle 

 duced into prominent forms low blunt process, 

 spine. 



Fronto-orbital width '64 ' Fronto-orbital width "59 

 that of carapace. that of carapace. 



Ischium of external maxil- Ischium of external maxil- Ischium of external inaxil- 

 lipeds without longi- lipeds with longitudinal lipeds with longitudinal 

 tudiual furrow. furrovN'. furrow 



Posterior carpal spine 

 (of cheliped) little 

 developed. 



Posterior carpal spine (of Posterior carpal spine (of 

 cheliped) sharp and ; cheliped) little deve- 

 well developed. ; loped. 



Ambulatory legs long and 

 slender. 



Ambulatorj' legs short 

 and stout. 



OcGU7'rence. — Nkata Bay, 23/6/04. Several specimens of medium 

 size. The Crabs were captured and brought me by the natives, 

 so that I have no direct evidence of their mode of life. They are 

 said to live in the water and not on land, though they sometimes 

 come on to the beach. 



Three small and immature specimens in the collection of the 

 British Museum (Reg. No. 91.12.19.1-3). Only the fohowing 

 particulars are given : — " Lake ISTyasa, Coll. Miss M. Woodward, 

 pres. by Miss Sophia McLaughlin." 



One rather small male, no precise locality given, British 

 Museum (Reg. No. 93.1.14.1). "Lake Nyasa. Received from 

 Mr. Joseph A. Williams, XJnivei\sities Mission, Likoma, Lake 

 Nyasa." 



One large female specimen, British Museum (Reg. No. 

 97.4.29.1). "West coast of Lake Nyasa from Ukala (?Nkata) 

 Bay to Ruarwe, June 1896." " A. Whyte collector — pres. by Sir 

 H. H. Johnston." 



A single large male specimen, collected by Mr. J. E. S. Moore 

 dviring one of his expeditions to Tanganyika, but without further 

 particulars. 



