IDIOSTROMA OCULATUM. 225 



with reproduction, and that they correspond with the " ampullae " of the Stylas- 

 terids and of Millepora. 



Obs. — Amphvpora ramosa, Phill. sp., being the only known species of the 

 genus Amphipora, I have nothing special to add to the above description of its 

 general characters. In an examination of a lai'ge number of transverse and 

 longitudinal sections of the species one is at once struck with the fact that 

 certain specimens (Plate IX, fig. 3, and Plate XXIX, fig. 5) are composed of a 

 comparatively dense central core of reticulated tissue, which is traversed by a 

 large axial canal, and is enclosed in a sheath of large peripheral vesicles bounded 

 externally by a delicate calcareous membrane. Other specimens, on the contrary, 

 have a generally more loosely reticulate structure, and have comparatively small 

 marginal vesicles, while an axial canal may apparently be wanting or imperfectly 

 developed (Plate IX, fig. 4, and Plate XXIX, figs. 6 and 7). Other examples, 

 lastly, appear to be completely devoid both of the marginal zone of vesicles and 

 of the external calcareous cuticle (Plate IX, fig. 4), though a well-marked axial 

 tube may be present. It seems most probable that these different forms are 

 really different conditions of a single type, though it must be admitted that at 

 present we have no decisive evidence in support of this view. 



I have never seen any example of Amphipora ramosa in which " Caunopora- 

 tubes " are developed. 



Distribution. — Amphipora ramosa occurs in great numbers in the Devonian 

 rocks of both Germany and Britain, marking a distinct horizon, which the German 

 geologists have determined as being in the upper portion of the Middle Devonian 

 rocks (the " Ramosa-banke " of Schultz). The Ampkipora-ramosa-beds of the 

 German Devonians are admirably seen at Hebborn (Paffrath district) and at 

 Hillesheim (in the Bifel). In Britain the species occurs abundantly in the 

 Devonian Limestones of Devonshire, at Shaldon, Newton Abbot, Teignmouth, &c. 



Genus 3. — Idiosteoma, Winchell, 1867. 



(Introduction, p. 99.) 



1. Idiostroma oculatdm, Nicholson. PL XXIX, figs. 8 — 11 ; woodcuts, figs. 



32, 33. 



Idiostboma oculatum, Nicholson. Mon. Brit. Strom., Introduction, p. 101, 



figs. 14 and 15, 1886. 



The ccenosteum in this form consists of slender cylindrical stems, from 3 to 10 

 mm. in diameter, which brancb and inosculate freely, so as to give rise to 



