A SYSTEMATIC AND STRUCTURAL ACCOUNT OF AYRAINYILLEA. 69 



young-growth forms conuected by an unbroken series with mature 

 forms of AvrtiinvUlea — in this case A. papmma. The C. pachypus 

 of Kjellman, from Labuan, is a hnk in the chain, having its 

 counterpart, however, in the Ferguson series. Tlie other species 

 of Avrainvillea which do not affect in any way the generic synonymy 

 will be found described in their proper place. 



The distribution of the genus is of some interest. It occurs 

 throughout tropical seas ; the West Indies and Brazil represent its 

 occurrence in the Atlantic ; the Eed Sea and Indian Ocean possess 

 forms of it, whence its distribution extends through the East 

 Indian Islands to the Pacific. The main point of interest lies in 

 the fact that the Atlantic forms (A. nigncans Decne., A. Iu7i(/icaulis 

 nob., A. sordida Crn. (excl. syn.), A. Mazei nob.) are confined to 

 the Atlantic, so far as is known; and the Eastern and Pacific forms 

 (A. pajmana nob., A. lacerata J. Ag., A. obscura J. Ag., A. comosa 

 nob., and A. caspitosa nob.) are also a group by themselves, not only 

 geographically, but fi'om the botanical point of view as well. 



The specimens occur in the shallow seas ; from no depth 

 beyond fifteen fathoms, so far as is known. In the practically 

 speaking tideless sea of the Antilles, Mr. Murray found A. lon/ji- 

 caulis and A. sordida Crn. most frequently at depths varying from 

 two to fifteen fathoms, but M. Maze records specimens from the 

 depth of 0)16 metre at Guadeloupe. Dr. Anderson found Aj.. papuana 

 at low-water mark in the Mergui Archipelago. According to 

 Harvey, A. cumosa occurs on coral reefs, but all the other species 

 appear to resemble the West Indian forms in preferring mud and 

 coral-sand. MM. Maze & Schramm say that specimens sometimes 

 occur on the shell of Strornhus <ji(jas. Mr. Murray founds. loiKji- 

 caulis occurring in great beds, the plants connected with each other 

 by a rhizome-like structure under the surface of the mud. It grows 

 most frequently in company with Zostera and species of Udotea. 

 Dredging for it was not a particularly successful operation, since 

 even a dredge specially designed for ploughing up mud-inhabiting 

 organisms (kindly lent him by the Scottish Marine Biological 

 Association) frequently broke oft' the fronds, and left the deeper 

 rhizoids behind. The best specimens were obtained by a skilful 

 negro diver (accustomed to dive for sponges, &c.), who was taught 

 without difficulty to distinguish Avrawvillea from Udotea (among 

 other matters) in situ, a performance which has not been equalled 

 by certain phycologists under far happier circumstances ! 



The systematic position of the genus is certainly next Penicillus, 

 and very near Udotea, to which it bears a strong resemblance as 

 seen with the naked eye. Unlike these genera, no species of 

 Avrainvillea has been found with an incrustation of carbonate of 

 lime, but it may be pointed out here that the amount of this 

 incrustation varies with the species in both Penicillus and Udotea. 



The following is a systematic disposition of the genus : — 



AVRAINVILLEA Decne. (Ann. Sci. Nat. Ser. 2, Tom. xviii. 

 p. 108, et Acad, de Paris Faculte d. Sci. 1842, p. 96). Alga marina 

 viridi-fuscescens, sessilis vel stipitata, ex fills non-septatis, cylin- 

 dricis vel moniliformibus, dichotomis, plus minusve intertextis 



