550 Prodronms of the 



Depastrum.* Gosse, 1858. 



According to Gosse's diagnosis and figures, this genus 

 is distinguished from Carduella, as I have characterized it, 



* Since I have had an opportunity to examine specimens of Carduella, I 

 liave compared it witli the descriptions of Depastrum as given by Gosse in " The 

 Aquarium'" and in his reclamation in the An. Mag. Nat. Hist. 1860, V., for June, 

 and with AUman's answer to the latter, from which I gather but one fact, or at 

 most two, which can now separate the two genera, and these are, in Depastrum 

 tiiere are no marginal anchors, and the tentacles arise at the margin of the disc or 

 without it. I offer the following suggestions and facts which have occurred to me 

 to be explanatory of what seem to be onlj' such differences as may be exhibited 

 by anyone individual. In the first place, in Sars' Fauna Litt. Norvegica, PI. 3, fig. 

 13, there is a distinctly octagonal area with a sharply defined boundary, the cor- 

 ners of which correspond to the ititertentacular spaces, and the sides to the groups 

 of tentacles which are without their margin; the marginal anchors are reverted 

 and inconspicuous, so that the prominent features are the octagonal area, and the 

 groups of tentacles outside the so-called margin are almost perfect counterparts 

 of Gosse's figure in the Annals and Magazine 1860, V. p. 481, fig. 3. Now in 

 Carduella, as I find and have described above, the margin of this octagonal area 

 corresponds to the inner or proximal ends of the short septa at the bases of the 

 tentacles and the marginal anchors, and which unite the oral and aboral sides of 

 the disc; but within this margin the two sides are free from each other, and very 

 naturally form a distinct fold along the line of separation, which fold constitutes 

 an octahedral figure with prominent angles. It is very easy to see now that if the 

 marginal muscle contracts in such a way as to revert the edge, as often I have 

 seen done in other Lucernarians, and at the same time constricts the urn below, 

 the octagonal area will inevitably become prominent; and this I suspect strongly 

 is the condition of the animal figured in profile by Gosse. (An. Jlag. 1860, V. 

 p. 481, fig. 2.) I would say also that it seems to me there must be a marginal 

 muscle outside the tentacles in Gosse's animal, else how could the neck of the urn 

 become so deeply constricted V My dissections have taught me that the marginal 

 muscle of Lucernarians is the extreme border of the oral side, without which the 

 tentacles do not originate, although they may arise close to its distal edge as ob- 

 tains in Halimocyathus. When, therefore, Gosse speaks of the tentacles springing 

 from the margin or without it, I take it that the margin is that of the octagonal 

 area, and not the true margin. The only serious objection to identifying the two 

 genera is that Depastrum has no marginal ancliors, according to Gosse. Now it 

 is notable, that Gosse's figure represents the animal in a contracted state, the 

 peduncle is strongly corrugated, the urn is deeply constricted, and the tentacles 

 are very short and thick set, as if, (and very probably), contracted. All this might 

 arise from an unhealthy state of the animal ; and Gosse remarks, that his specimen, 

 after being detached, did not refix itself, but laid at length on the bottom of the 

 vessel in which it was placed. In an unhealthy state the thick laj-er of lasso-ccUs 

 of the knob of the tentacles falls away very readily, and next sloughs off the 

 outer wall of the shaft, thus leaving the thick musculo-gelatiniform layer exposed. 

 Now if this were to happen to the short marginal anchors of Carduella there would 



