MUSEUM OF COMPARATIVE ZOOLOGY. 13 
Acanella Gray (emended). 
Acanella Gray, Cat. Lithophytes Brit. Mus., 1870, p. 16. 
Coral either simple or variously branched. Axis with long calcareous joints 
and very short horny ones. The branches, when they exist, arise from the horny 
joints, either singly or two or more together, sometimes forming whorls. Ccen- 
enchyma very thin, containing, more or less abundantly, elongated fusiform 
spicula, usually of large size. Calicles large, elongated, composed of large, fusi- 
form spicula, often obliquely arranged; the margin is armed by about eight long, 
spine-like, projecting acute spicula. Tentacles stiffened by abundant spicula. 
Base, in most cases, divided into large, flat, palmate lobes, which descend into 
the mud and serve as supporting roots or anchors. 
This genus, as established by Gray, for A. arbuscula Johnson, had as one of 
its most prominent characters the verticillate arrangement of the branches. 
The discovery of several closely allied species without this peculiarity, one of 
them being entirely simple, shows that the mode of branching, as in most 
other genera of Gorgonacea, is only a specific character. 
The relation of this genus to Isidella Gray is still doubtful, for the nature of 
the coenenchyma and calicles of the type-species of the latter was unknown to 
Gray. Indeed, the precise species which he had in view is very doubtful, 
although he referred it to I. elongata Esper, a species that had never been 
properly described, and which could not be positively identified, as it was 
based on the axis only. The species described under the same name by 
Philippi is probably a distinct species, having elongated calicles, with long 
projecting spicula, as in Acanella. 
I have hitherto referred to I. elongata, a species procured at Naples, many 
years ago, by Professor J. D. Dana, and of which several specimens, consisting 
of the axis alone, are in the Museum of Yale College. So far as the axis 
shows, these might belong either to Acanella or to Lepidisis, or to a genus dis- 
tinct from either. 
Koch has described a species, perhaps the same, under the name of Zsis 
Neapolitana, which may be the species intended by Gray as the type of Jsi- 
della, and which is apparently the same as my I. elongata from Naples. In 
this species the calicles are not furnished with the projecting spicula, so con- 
spicuous in Acanella and Lepidisis. The corresponding spicula are present, 
however, according to the figures given by Koch, as fusiform spicula, larger 
than the others, but not projecting beyond the margins of the elongated cal- 
icles. The ccenenchyma is thin, and contains small fusiform spicula. This 
species is, therefore, closely allied to Acanella, the principal difference being 
the less development of the marginal spines of the calicles. Possibly this may 
be the species called Isidella elongata by Gray, but it would be difficult to prove 
it. Therefore it might be best to reject the name, Jsidella, as not recognizably 
established. Otherwise it might be restricted to such species as I. Neapolitana 
and I. borealis (= Mopsea borealis G. O. Sars), in which the marginal spines are 
not much developed and do not project. 
