57 



as the Mediterranean, but is often' quite undivided; and where branches are found, they are 

 very few in number, simple (not again divided) and extended in different directions (not in 

 the same plane). Finally the calcareous joints are in our species remarkable from their 

 unusual length, while the horny joints are quite short. In the Mediterranean species the 

 calcareous joints are, according to Philippi, at most 8 lines long, and the horny joints 2 lines 

 long; thus the proportion of relative length is at most but as 4 to 1; while in our species it 

 is usually as 1520, and in younger specimens often as 30 40 to 1. Further there seems 

 to be some difference in the spicula. Philippi describes, besides the shorter ones, 8 very 

 long lancet-shaped spicula, which in dried specimens extend far beyond the calyx in the form 

 of 8 regular points (according to Risso's figure these points are even more than half as long 

 as the polyp). Such unusually long projecting and regularly arranged spicula are not found 

 in our species. 



Finally our species seems, by the elongated form of its calcareous joints, to resemble 

 the species shortly noticed by Pourtales l Mopsea eburnea from Florida; but this is like the 

 other Isidinee dichotomically branched, and differs besides in the calcareous joints not being 

 thickened at the extremities, as is always the case with the larger joints in our northern 

 species. The above described characteristic lobed form of the root has been hitherto, among 

 the Isidinse only observed in the Mopsea elongata, in which it is described by Philippi in a 

 very similar manner; although its lobes or branches are according to this naturalist exter- 

 nally quite smooth, which as above mentioned, is not the case in our species ; the latter 

 having them very distinctly marked with longitudinal stripes. 



I shall in conclusion remark that in all probability we have yet another species of 

 Isidinse on our coasts. The learned Bishop Gunnerus of Throndhjem has, in ,,Det kongl. 

 Xorske Videnskabers Selskabs Skrifter" Vol. 4. 1768 Tab. 4. Fig. 8. delineated a piece of a 

 stem taken up from the sea off Sinolen, which he considers to have belonged to an Isis 

 hippuris. But as this coral is an evident tropical form, only known from. East India, there 

 can be no question of our having the same species in our seas. The peculiar form of the 

 calcareous joints and their unusual shortness in comparison with the horny joints, seem also 

 decidedly to oppose the notion that this piece should belong to the species here described, 

 Mopsea borealis, and rather to shew that it belongs to some species of the real genus Isis. 



1 Bulletin of the Museum of Comparative zoology at Harvard College. Cambridge No. 7. 1868. p. 132. 



