REPORT ON THE ALCYONARIA. 73 



Genus 6. Plumarella, Gray. 



Plumarella, Gray, Cat. Lithophytes Brit. Mus., 1870, p. 36. 



Plumarella, Studer, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 1870, p. 648. 



The genus Plumarella was established by Gray for Gorgonia penna, Lamk., a 

 Primnoid from the neighbourhood of New Holland. The diagnosis runs, "Coral fan- 

 shaped, forked, expanded, branchlets pinnate, opposite or alternate. Bark thin. Cells 

 elongate, elavate, incurved, alternate, in two rows on each side of the stem. Axis 

 continuous, stony." 



Studer {loc. cit.) expanded the diagnosis in order to include in the genus Plumarella 

 hilgendorfi, Stud., from Japan. This latter, however; on comparison with the greatly 

 increased material now at command, must be relegated to Thouarella, and thus 

 Plumarella is referred to in the sense used by Gray. 



If we consider Gorgonia pemia, Lamk., as the type of the genus, and as represented by 

 a magnificent specimen in the Museum of the Jardin des Plantes in Paris, then we may 

 include in the same genus several more species ; thus Primnoa pourtalesii, Verrill, 

 recently described by Verrill,' and a new species obtained by the Challenger, may be 

 included. Cricogorgia 7*a?7iea, figured by Milne-Edwards' but not described, seems to 

 be identical with Lamarck's Gorgonia 2)enna. 



The stem is upright, greatly ramified in one plane, so that the whole colony acquires 

 a fan-like appearance. The expression " forked " used by Gray regarding the stem is not 

 correct. The stem does not undergo a dichotomous forking, but is produced continually, 

 only it gives ofi" occasionally from two sides lateral branches, which may attain the 

 strength of the main stem, and at the point of departure of the branch from the main 

 stem this latter generally undergoes a twist in the opposite direction. The same takes 

 place with the twigs of the branches, and the impression of a dichotomy may thereby 

 arise. The main stem, as well as the stouter branches, are always flattened in the same 

 plane as that of the expansion of their twigs. The axis is brittle, calcareous ; it first 

 becomes softer and horny in the thinner twigs, yet it always maintains a relatively strong 

 rio-idity. Branches come off from two sides of the main stem in an ascending series, 

 generally alternating ; they are partly thin, rod-like, simple, partly strong, with flattened 

 axis and branched. They run parallel to one another. The branches give off lateral 

 twdgs again in like manner, which are sometimes simple, sometimes again give ofl' thinner 

 twigs. The last twigs are thin, rod-like structures. The calyces are generally small, 

 cylindrical, and arise in alternating series from the branches and twigs, generally at 

 relatively great distances from one another. The calyx scales are thin, cycloid, with 

 central nucleus, the prominences small, smooth, the edge finely toothed. The operculum 



1 Bull. Mus. Comp. Zool., vol. xi. No. 7, 18S3, p. l8. 



2 Hist. Nat. des Coralliaires, Atlas, pi. B. 2, fig. 6. 



(zOOL. CHALL. EXP. — PART LXTV. — 1887.) SsS 10 



