1889.] ON NEW OR RARE SPECIES OF PLEXAURIDS. 47 



4. Descriptions of some new or rare Species of Plexaurids. 

 By F. Jeffrey Bell, M.A., Sec, R.M.S. 



[Eeceived January 28, 1889.] 

 (Plate III.) 



Among the Gorgonids in the British Museum there are examples 

 of some species of the genera Plexaura and Plevaurella which 

 appear to be still undescribed. As to a number of the described 

 species, it is often impossible to say with certainty whether or no 

 one has them before tlie eyes; Milne-Edwards and Haime, like 

 Duchassaiiig and Michelotti, make no use of the characters of 

 the spicules, though the works of both were published afcer the 

 appearance of Valenciennes's suggestive essay '. Fortunately the 

 Britisli Museum is in possession of a series of preparations by 

 M. Potteau which may be regarded as illustrative of Valenciennes's 

 memoir, and by the aid of these it is often possible to add enough to the 

 otherwise imperfect diagnoses of tlie earlier describers of these forms. 



Of the species now to be described it may be said that they have 

 all such well-marked characters that it is unlikely that any previous 

 description of them can have been overlooked. One of them will 

 always rank with the most splendid memi)ers of a group which, as 

 all know, contains so many remarkable and beautiful forms ; another 

 was long since recognized to be a distinct species by the late Dr, Gray. 



1. Plexaura principalis. (Plate III. fig. 1.) 



An exceedingly fine form ; the whole colony a large bushy mass of 

 a uniformly light-brownish colour. Allied to P. sufruticosa, but 

 rather less ramose, the terminal branches longer, the branches not 

 so flexuous and very rarely nodose ; calyces not so closely packed. 



The specimen under description is 80 cm. high, r38 m. in spread ; 

 the base is flattened from side to side, and its long axis is at right 

 angles to the chief plane of spreading ; the greatest length of the axis 

 is about 90 cm. The primary trunks are flattened, vary in size and 

 are only seldom swollen ; the terminal branches are rounded, and 

 are often, though not always, about 10 cm. long. The orifices of 

 the calices are rather small ; they are generally at.out 1 mm. apart, 

 but sometimes they are separated by 2 mm., and occasionally they 

 are a little more distant from one another. Cortex smooth, mode- 

 rately thick ; axis black, not very flexible. 



The characters of the cortical spicules may be best made out from 

 the accompanying figures^; for the purpose of comparison the 

 s]nc\i\es o{ P. sii^ruticosa are, now for the first time, figured; the 

 chief points to be noted are that P. imperialis appears to have no 

 spicules of the so-called " Blattkeule " form ; the fonr-rayed spicule 

 is rare, and is either vestigial or rudimentary in character. The 

 elongate spicules are longer and more delicate than in P. svffruticosa ; 



1 Comptes Eendus, sli. p. 7 et seq. 



^ All the spicules figured in the accompanying drawings (Plate III.) are 

 magnified about ISO times. 



