200 ON THE OCCURRENCE OF MESENTERIPORA, 



The genus Mesenteripora was established by Blainville (Manuel 

 d'Actinologie) for one recent and several fossil species of Poh/zoa 

 which he regarded as allied to Eschara. Milne-Edwards (Ann. 

 des Sci. Nat. 2d serie, tome ix., p. 226, 1838) pointed out their 

 true affinities with the Cyclostomata, and D'Orbigny in 1852 

 (Prodr. de Palseont. stat.) described several fossil species from 

 the Cretaceous of France, and subsequently (Paleontologie 

 Francaise, tome v., 1852) added descriptions and figures of several 

 more fossil species. In 1844, S. Wood (Ann. and Mag. Nat. 

 Hist., xiii., p. 14) had described a fossil species from the Crag 

 which he named Diastopora meand/rina ; this species was afterwards 

 described and figured by Busk (Fossil Polyzoa of the Crag, p. 

 109, pi. xvii., fig. 2, pi. xviii., fig. 4, and pi. xx., fig. 2 — 1859), 

 and is said to have been obtained in the recent state off the coast 

 of Greenland by Tor ell. 



In the species described by Blainville, Milne-Edwards, Wood, 

 and D'Orbigny, the polyzoarium assumed a lamellate-foliaceous, 

 erect character, which induced the first named author to regard 

 the genus as having a place in the Escharidce. In the Australian 

 variety on the other hand the polyzoarium never seems to assume 

 this form. It is primarily flat and encrusting, growing outwards 

 in a radiating or fan-like manner from the primary cell. In this 

 stage the general form of the polyzoarium is very similar to that 

 of Tuhulipora, and closely resembles the young stage of 

 Mesenteripora meandrina as figured by Busk (1. c, pi. xx., fig. 9). 

 At the periphery the cells are three or four deep, the upper ones 

 sometimes free to a slight extent, but never very prominent ; 

 wherever the lower layers come in contact with an obstacle (such 

 as a Serpula-tube) there is a tendency in the upper cells to take 

 a direction almost vertically upwards. The marginal cells are 

 usually bilabiate, the lips being generally unequal and acute, 

 but sometimes the peristome is circular and entire. The cells of 

 the upper la3'er as the margin grows out beyond them become 

 less prominent, though still projecting a little above the surface 



