394 Dr. F. Miiller o?? Balanus armatus. 



could be cletcrmiried as l)elonging to a large sulphur-yellow 

 Fcqnih'na not uncommon here. This Papillina (and perhaps, 

 indeed, the whole genus PajJiUina^ Schmidt), however, is no- 

 thing but a Vioa which takes up its abode in shells and other 

 calcareous structures, penetrates them, and in course of time 

 almost entirely destroys them, and, finally growing over them, . 

 increases into large cake-like masses, which may attain a dia- 

 meter of more than a foot. It was therefore doubtful in this 

 case whether the Balanus had sought out tlic Sponge, or the 

 Sponge the Balanus^ especially as the shells were attacked by 

 the Sponge in several places. 



Subsequently I have frequently found Balanus armatus in 

 abundance in a Reniera which, in shape, colom*, and form of 

 spicules, closely approaches R. aquceductus^ Schmidt, and is 

 particularly characterized by its greatly developed fibrous 

 framework, which is as readily washed out as that of the 

 common sponge. Very rarely (I have as yet only once found 

 three specimens) the Balanus occurs in one of our commonest 

 sponges, which coats whole rock-walls in the form of a dark- 

 red mass beset with steep, jagged, mountain-like protuberances, 

 and in its hard structure approaches Reniera digitata^ Schmidt, 

 On the contrary, it is frequent on an eight-rayed polype, 

 Ca7'iJoa rupicola^ F. Mlill.*, which grows at the depth of 



* Carijoa i-ujncola (fig-. 5(3). The eutire stem of the polyparv (which 

 attains a height of 0"15 metre, rising straight or slightly curTed, and is 

 ahout 2 millim. in thickness, is formed by a single polype, which unfolds 

 its tentacles at the extremity, and the body-cavity of which penetrates 

 the whole stem. The polype can retract itself into the upper extremity 

 of the stem. This retractile part is snow-white. The pkmiose tentacles 

 are produced into a thin terminal filament, which appears nodose, like 

 the slender lateral appendages. Beneath the- circlet of tentacles there are 

 some delicate calcareous spicules. The dissepiments surromiding the 

 stomachal tube are continued throughout the whole length of the hollow 

 stem as eight slightly projecting longitudinal lines : tAvo of these, lying 

 close together, bear an undulated membranous border with a thickened 

 margin, in which the dark brownish-violet ova are developed, likewise 

 throughout the whole length of the stem. The wall of the stem below 

 is sometimes as much as O'o millim. in thickness ; above, it becomes 

 thinner and flexible ; in the lower part the stem appears smooth ; in the 

 upper, softer portion it is traversed by eight longitudinal fm-rows. There 

 are no projecting calcareous spicules. The wall acquires firmness by 

 closely approximated calcareous spicules, which are deposited in all pos- 

 sible directions in planes parallel to the axis. These are straight or 

 slightly curved, irregularly beset with more or less numerous knots : 

 some of them are longer (average 0-25, single ones more than 0-5 millim.), 

 slenderer, and smoother than the rest ; the others, which pass into the 

 former by intermediate forms, are shorter and stouter, and beset with 

 more numerous and stronger processes. The latter occur here and there 

 fused together. 



From the stem spring numerous branches, usually four or five, at nearly 



