On the Rhizocephalan Genus Thompsonia, etc. 



29 



ment probably parthenogenetic. Nauplius stage omitted from life-history, 

 larvae liberated at Cypris stage, after disintegration of the visceral mass, 

 through apical cloacal aperture which appears in the mantle at a late stage. 

 Moulting of host not prevented. 



I will quote here the original description of Kossmann (6, Taf. v, 

 Fig. ii a) : 



"Die Thompsonia globosa entbehrt einer Manteloffnung. Dagegen besitzt 

 sie einen ,ausserordentlich langen Russell, welcher etwa in der Mitte seiner 

 Lange einen Ring verdickter Cuticula zeigt. Der Korper des untersuchten 

 Thieres war ganzlich reducirt, die Bruthohle aber angeftillt mit Larven des 

 Cypris stadiums, welche zwei Augen besassen. Die grosse des Thiers war 

 sehr gering: 1.8 mm. Lange incl. des Riissels zu 0.75 mm. Breite. Die 

 beiden Exemplare nach welchen die obige liickenhafte Beschreibung gemacht 

 ist, sassen beide, nicht am Abdomen, sondern an den Beinen einer Melia 

 tresselata. Fundort, Aibukit, Palaos." 



THE SPECIES OF THOMPSONIA. 



The following is a list of the species which have been described up 

 to the present: 



This list does not include the parasite mentioned by Spence Bate 

 as occurring on Alpheus digitatus from Fiji. It appears to be a species 

 of Thompsonia. 



I next give a tabular statement of the forms of Thompsonia which 

 I have seen myself and the characters in which they differ : 



Species on which the 

 forms occur. 



Localities. 



Differences in characteristics. 



Synalpheus brucei . . . 



Actaea ruppellii 



Thalamita prymna. . 



Murray Island, Torres Straits. . 



South Africa 



Murray Island, Torres Straits. . 



External sac, pear-shaped, pink, 1 

 mm. long. Cypris. 



External sac, pear-shaped to round, 

 1 mm. long. 



External sac, elongate, lemon-yel- 

 low, 3 mm. long. Cypris. 



