Madreporan'on Genus Tuibliuiria. 501 



Earliest Cup-Stage of Turbinaria. — The corallum of the 

 genus Turbinaria is somewliat peculiar in the fact tliat it 

 typically a])pear3 in its earliest stage as a small cup. This 

 cup-stage is, however, generally transitory. As the edge of 

 the cup grows, its shape gradually changes in various ways 

 presently to be described. This important fact has, I believe, 

 never been thoroughly, if at all, recognized. The cup-shape 

 of the corallum was thought to be a specific* distinction, and 

 not wliat it really is, viz. merely a phase in the ordinary 

 development of the sj)ecimens of this genus. The confusion 

 this has caused in the arrangement of the Turbinarians may 

 be more easily imagined than described. 



Before, however, discussing the systematic arrangement of 

 the genus, which must for the future be based upon this fact 

 — that every corallum begins typically as a cup — it will be 

 well to describe the method of budding to which this peculiar 

 method of growth is to be attributed. 



The earliest development of Turbinaria I have not had 

 any opportunity of working out, and all my conclusions have 

 been drawn from an examination of the specimens in the 

 National Collection. Among these are a great number of 

 very miimte cups, ranging from 1 inch across, and standing 

 on stalks from 1 inch high. The stalk is always slightly 

 expanded wliere it adiieres to the substratum. 



The Stalk and the Axial Polyp. — A cross section through 

 a stalk of a minute cup reveals a single rather large polyp- 

 cavity, surrounded by a thick spongy wall which shows an 

 irregular series of radiating plates (costaj) bound together by 

 irregular concentric synapticulaj ; near the surface the radiat- 

 ing plates project as the ridges which run longitudinally down 

 the surface of the stalk (Pl.^XlX. tig. 1). 



This central polyp-cavity in the stalk is the parent polyp 

 of the young corallum, and the spongy coenenchyma is a 

 simple thickening of its walls by the outward radial growth 

 of costs, which at more or less regular intervals are bound 

 together by concentrically arranged synapticular |)lates. Sur- 

 rounding thecentral cavity, then, there is aseries of longitudinal 

 canals running parallel with the polyp-cavity. All these are 



catory Value of Growth and Budding in the Madreporidne, an 

 a new Genus illustrntinp this Point," Ann. & Mag. Nat. Hist, vol 



and on 

 a new Genus illustrntinp this I'oint," Ann. & iMag. JNat. Hist. vol. xiii. 

 (1884) ; and A. Ortniann, " Die Morphologie des Skelette.s der Stein- 

 korallen in Beziohung zur Kolouiebildung," Z. wi.ss. Z. Bd. 1. (ISUO). 



• Ehrenberg appears to have made it a generic distinction. He re- 

 vived Oken'.s genus 'JKrhiuavia lor the stalked forms, and retained 

 Lamarck's gi nus Jirplaiiaria for e.xplanate specimens in which, if Tur- 

 binarians, the stalk had been <ib.>-cured. 



