2 34 



Turèinaria). The new species from the Malay Archipelago, which will be described in this 

 report, are also inhabitants of shallow water. 



According to Darwin, Acasta is always embedded in sponges, or in the sponge-like 

 outer layer of the skeleton of /sis. Annandale took his new species from the surface of Tur- 

 èinaria, a Madreporarian coral. KrüGER does not inform us from what host his new A. Dojlciui 

 was taken. Weltner's A. scuticosta was found living in a sponge: Tethya lyncurium Johnst. 

 Gruvel, with regard to his new species, A. str/a/a, only says that it was "ramenée d'une 

 profondeur de 400 mètres". With regard to the Siboga-species, A. glans from Pepela-Bay, 

 Rotti-island, was handed to me disengaged from the sponge in which, presumably, it was 

 originally found embedded ; the other specimens of this species, which were collected by the 

 Dutch Fishery Inspection-Steamer "Gier", are still partly covered by pieces of sponge. A. conica 

 n. sp. came into my hands with the sponge in which it is embedded. The surface of the latter 

 shows almost quite globular excrescences, with a small oval opening at the tip, and the Acasta 

 is found in this excrescence, the aperture of its opercular valves corresponding exactly to the 

 opening of the sponge. The specimens of A. nitida n. sp. were taken out of the sponge 

 and even quite clean when they came into my possession. 



A few worcls may be said here on the peculiar position of the genus Acasta in 

 the classification of the Sessile Cirripedes. Darwin considered it as a Sub-Ge nus, without 

 saying exactly what he meant by that term and "hoped" he might stand excused for 

 admitting it as such. According to him the species of this genus, in the structure of the 

 shell, and in all the characters derived from the opercular valves and animal's body, cannot 

 properly be distinguished generically from some species of Ba/anus. He pointed out that 

 some species of the latter genus (B. navicula and B. cymbiformis) agree in all essential 

 respects with Acasta, and differ only in the shell being more elongate and in being attached 

 to Gorgoniae instead of to sponges; Acasta purfturata, however, lives embedded in the 

 outer layer of the skeleton of /sis, so that even the habit of living embedded in sponges 

 fails in that species. There are, on the other hand, species of Balanus (B. spongicola, 

 B. dcclivis) that inhabit sponges .... Darwin finished by saying that the most important 

 character of Acasta probably consists in the anterior ramus of the fourth pair of cirri 

 differing slightly in the arrangement of its spines, and in some other points, from the rami 

 of the posterior pairs of cirri, and considered this as a character not as yet observed in any 

 other Cirripede. 



As I pointed out when discussing the difficulties of subdividing the genus Balanus, 

 this very same character is observed, however, in further species of Balanus, and, certainlv, 

 the validity of the genus Acasta has not been strengthened by this discovery. But, on the 

 other hand, the present known species of Acasta seem together to form a very natural group, 

 characterized by the thinness of the parietes in which pores are absent, by the great develop- 

 ment of the radii, by the cup-formed basis and by their living — ■ with a single exception - 

 embedded in sponges. Therefore I would not consider it an advantage to cancel this genus 

 and to include its species in the genus Balanus, however closely related the two genera 

 may be. Perhaps a thorough study of sumciently rich material of those species of Balanus 



106 



