The Genus Porosphccra, Steinmaun. By George J. Hinde. 21 



others, sometimes also there are two or more slight elevations to 

 which the grooves converge (pi. I., fig. 18). There are no special 

 apertures at the point of convergence beyond the openings of the 

 minute radial canals, which are present all over the surface, alike 

 on the ridges and the grooves. 



As in P. globulavis, a number of these sponges are penetrated 

 by cylindrical tubes which extend either longitudinally or trans- 

 versely through them; of those which I have examined about 

 17 p.c. are traversed by tubes. The sponges range from 4 to 

 20 mm. in diameter. 



The spicular structure of the skeletal fibres appears similar 

 to that of P. globulavis, and the same may be said of the dermal 

 layer, fragments of which, however, were only observed on the 

 surface of two specimens. 



From P. globidaris, this species is distinguished by its form 

 and the ridges and grooves of its surface ; and from P. Woodwardi, 

 Carter, by the absence of a concave base of attachment and by 

 the great difference between its shallow simple grooves and the 

 branching canals of P. Woodwardi. Specimens of P. nuciformis 

 have been generally referred to Carter's species, but this latter is 

 rare, and it seems to me a quite distinct form, and, moreover, it 

 is restricted to a lower zone than that in which P. nuciformis 

 occurs. 



Von Hagenow considered that the pear-shaped specimens of 

 nuciformis which he figured were only more perfect examples of 

 the spherical forms, that is of P. globularis, Phillips, of which 

 he makes no mention, and he evidently intended to include both 

 in the species nuciformis. If this w r ere the case, Phillips' name 

 would have the priority, but it seems to me that the pear-shaped, 

 grooved forms differ specifically from P. globularis, and I propose 

 to retain for them Hagenow' s name nuciformis. 



Distribution. — P. nuciformis makes its first appearance in the 

 zone of Micraster cor-anguinum at Croydon, coast of Thanet and 

 Dorset, and at Flamborough ; it is relatively more numerous in 

 the zone of Marsupites at Margate and the Thanet coast, and 

 reaches its maximum in numbers, and size in the zone of Act. 

 quadratus at and near Newhaven, near Brighton, and the Isle of 

 Wight ; it is also numerous in the zone of Bel. mucronata at 

 Ballard Cliff and Studland Bay, Dorset, and likewise occurs at 

 Trimingham, Norfolk coast. Abroad it is found in the Chalk 

 of Riigen. 



o v 



PorospJiaTa Woodwardi, Carter sp. (pi. I., fig. 19). 



1877. (?) Bradya tergestina, Carter (non Staclie), Ann. and Mag. Nat. Hist., 



ser. 4, vol. xix., p. 64. 



1878. Millepora Woodwardi, Carter, op. cit., ser. 5, vol. i, p. 306, pi. xvii., figs. 6 8 . 



