South African Crustacea. 51 



1905. Astacillidce, Stebbing, Herdman's Eep. Ceylon Pearl Fisheries, 

 pt. iv., Isopoda, pp. 43, 46. 



This family, as at present constituted, includes the genera Asta- 

 cilla, Cordiner, 1793, Arcturus, Latreille, 1804, Arcturella, Sars, 1897, 

 Antarcturus, zur Strassen, 1902, Pleuroprion, zur Strassen, 1903. 

 Arcturides, Studer, has been transferred by Ohlin to a different 

 family. In establishing Arcturella for his own Astacilla dilatata, 

 Sars speaks of that as being " as yet the only known species of the 

 genus." But I am inclined to think that both Leachia nodosa, Dana, 

 1849, and its close ally, Arc turns corniger, Stebbing, 1873, ought to 

 be also referred to it, as well as Arcturus damnoniensis , Stebbing, 

 already transferred by Norman in 1904. In 1902 zur Strassen trans- 

 ferred all the species from tropical and southern waters at that date 

 reposing in the genus Arctums, a score in number, to his new genus 

 Antarcturus. If this cleavage be accepted, it will probably be 

 followed by further generic subdivision, when some of the species 

 have been described in more detail. Miss Harriet Eichardson has 

 given an analytical key to the North American genera of the family, 

 among which Arcturella and Antarcturus are not included. In Asta- 

 cilla and Arcturella the marsupiurn of the female is formed by a 

 single pair of plates attached to the fourth perseon segment. In 

 Pleuroprion Miss Eichardson gives the character, "marsupiurn as in 

 the genus Arcturus." But here a difficulty arises. According to Sars 

 and Eichardson, in Arcturus the marsupium is composed of three 

 pairs of plates issuing from the second, third, and fourth segments of 

 the perseon. Studer and Beddard, on the other hand, assign to this 

 marsupium four pairs of plates, Studer in 1884 carefully figuring 

 and describing the four pairs in the female of his Arcturus furcatus. 

 This is in agreement with the new species about to be described. 

 Unfortunately several species may have been assigned to Arcturus 

 or Antarcturus without determination of this character. In such 

 cases as those of Beddard's Arcturus spinifrons and Arcturus myops, 

 when only males or what appeared to be males were obtained, such 

 determination was obviously out of the question. Neither for 

 Antarcturus oryx nor for Pleuroprion chuni, the typical species of 

 his new genera, does zur Strassen give the number of the marsupial 

 plates. It is therefore with some reserve that this character is 

 employed in the following key : 



I Marsupium formed by one pair of plates 2. 

 ' | Marsupium formed by more than one pair of plates 3. 



f Fourth perseon segment much elongated 1. Astacilla. 



I Fourth perseon segment not much elongated 2. Arcturellu . 



