22 Mr. H. J. Carter on the Sicbsjjherous Sponges. 



cells which I have found and described in the chambers of 

 OpercuUna arahica^ and which in some specimens of tliis test 

 in my possession may be seen (for they appear to be the same) 

 on their way out from the introseptal canals, or at the orifices 

 of holes in the spire, covered with a coating of white calcareous 

 matter. What the real nature of those supported on the trifid 

 spicules of Tethya arabica may be I must leave future ob- 

 servation to determine. 



8]Jicules. 



In describing the spicules, it is very desirable to state 

 whether they are straight or curved, as they maintain this 

 characteristic feature throughout in the species which I have 

 described, whatever their other forms may be. In vain we 

 look for this in the specimens of " specific description " pro- 

 posed by Dr. Bowerbank (Phil. Trans. 1862, p. 1132) for 

 " adoption by naturalists," and, of course, followed in his in- 

 dividual descriptions. 



Now in Tethya arabica and Tethya lyncurium^ as may be 

 observed by the illustrations &c., they are all straight, whereas 

 in Geodia arabica and Pachyviatisma Johnstonia they are all 

 curved, however varied in other respects. 



When we look for a figure of the spiculum of the latter in 

 Dr. Bowerbank's illustration of Pachymatisma (Phil. Trans. 

 1862, pi. 72. fig. 6, and Brit. Spong. fig. 353), we find the spi- 

 cules there not only almost all straight, but for the most part 

 also pointed at each end, instead of being all curved in the 

 shaft and round or inflated at the ends ; so that one is tempted 

 to doubt if it be a figure of this sponge. 



Again, when we turn to the two figures of Geodia Barretti 

 in the Phil. Trans, (pi. 72. fig. 5, and pi. 32. fig. 2), the latter 

 of which is repeated in the Brit. Spong. fig. 354, we find fig. 2 

 three times as large as fig. 5, and the " radii of the patento- 

 ternate" spicules in fig. 301 (Brit. Spong.) still larger; yet 

 they are all set down as " x 50 linear." Which is the true 

 representation? Generally speaking, these illustrations are 

 beautifully executed ; but of their truthfulness are we to say, 

 after having only examined one or two of them, ex uno disce 

 omnes ? 



Had Dr. Bowerbank drawn these figures himself, these 

 mistakes could hardly have occurred ; neither ought they to 

 have come before the public so untruthful under any circum- 

 stances. 



But the plan throughout pursued by Dr. Bowerbank, in his 

 description of the Spongiada3,can never suffice for the subject. 

 Mere magnified views of the elementary parts alone of objects 



