On the Rhizocephalan Genus Thompsonia, etc. 29 
ment probably parthenogenetic. Nauplius stage omitted from life-history, 
larve 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. 1 a): 
“Die Thompsonia globosa entbehrt einer Manteloffnung. Dagegen besitzt 
sie einen ausserordentlich langen Riissell, welcher etwa in der Mitte seiner 
Lange einen Ring verdickter Cuticula zeigt. Der Kérper des untersuchten 
Thieres war ganzlich reducirt, die Bruthéhle aber angefiillt mit Larven des 
Cypris stadiums, welche zwei Augen besassen. Die grésse 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: 
Place. Lenth of external 
sac. 
Host. 
Thompsonia globosa Kossm....| Melia tessellata Aibukit Pelews...| 1.8 mm. 
Thompsonia (Thylacoplethus) | Alpheus edwardsi....| Thursday Island, 
edwardsi Cout. Torres Straits. 
Thompsonia (Thylacoplethus) | Alpheus macrochirus | Fernando Veloso..| 4.5 mm. 
heurteli Cout. | 
Thompsonia (Thylacoplethus) | Alpheus avarus Torres Straits....| 1 mm. (young). 
sp. 
Thompsonia japonica Hiifele. .| Pilumnus sp 2mm. elongated. 
Pagurus striatus.... .| 
Thompsonia affinis Kriiger....; Diptychus sp Ja 1 mm. round. 
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 
Localities. Differences in characteristics. 
forms occur. 
Synalpheus brucei. . | Murray Island, Torres Straits..| External sac, pear-shaped, pink, 1 
mm. long. Cypris. 
Actea ruppellii South Africa External sac, pear-shaped to round, 
1 mm. long. 
Thalamita prymna..| Murray Island, Torres Straits..| External sac, elongate, lemon-yel- 
low, 3mm. long. Cypris. 
