Madreporarian Oenus Turbinaria. 501 



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

 genus Turhinaria is somewhat peculiar in the fact that it 

 typically appears 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 what it really is, viz, merely a phase in the ordinary 

 development of the specimens 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 Turhinaria 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 minute cups, ranging from 1 inch across, and standing 

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

 expanded where it adheres to the substratum. 



The StaJk 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 (costa?) bound together by 

 irregular concentric synapticula? ; nekr the surface the radiat- 

 ing plates project as the ridges which run longitudinally down 

 the surface of' the stalk (PI. XIX. fig. 1). 



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

 of the young corallum, and the spongy ccenenchyma is a 

 simple thickening of its walls by the outward radial growth 

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

 together by concentrically arranged synapticular plates. Sur- 

 rounding thecentral cavity, then, there is a series of longitudinal 

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



catory Value of Growth and Budding in the Madreporidfe, and on 

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

 (1884) ; and A. Ortmann, " Die Morphologie des Skelettes der Stein- 

 korallen in Beziehung zur Koloniebildung," Z. wiss. Z. Bd. 1. (1890). 



* Ehrenberg appears to have njade it a generic distinction. He re- 

 vived Oken's genus Turbinaria for the stalked forms, and retained 

 Lamarck's genus Explanaria for explanate specimens in which, if Tur- 

 binarians, the stalk had been obscured. 



