LEPTOPHRAGMA.— PLEUROSTOMA. 103 



Cup- or funnel-shaped sponges, with walls from 1-5 to 2 mm. in thickness. 

 Variable in size ; an average specimen measures 100 mm. in height and 75 in width 

 at the summit. 



The canal-apertures of the outer surface are circular and very regularly disposed 

 in vertical and horizontal rows ; they are about -5 mm. in Avidth, and about the same 

 distance apart. 



The spicular mesh has been replaced by peroxide of iron or dissolved away, and 

 is very indistinctly shown. 



Distribution. Upper Green Sand (I) : near Folkestone. Lower Chalk: South of 

 England. Upper Chalk : Haldem, Germany. 



Leptophragma feagilis, Bcemer, sp. 



1840. Scyphiafragilis, F. A. RcEmer, Nordd. Kreide, p. 8, t. 3. f. 11. 



1877. Leptophragma fragilis, Zitt. Studien, I Ab. p. 48; Neues Jahrbuch, p. 358. 



Sponge in the form of a shallow, open cup supported on an elongated cylindrical 

 stem. One specimen, imperfect at the margins, is 90 mm. in width ; in another 

 specimen a stem 80 mm. in length and 65 in width, supports a portion of a cup. 



The walls are only -5 mm. in thickness ; their surfaces are closely covered with 

 minute canal-apertures -25 mm. wide, disposed in rows, or irregular in their distri- 

 bution. The mesh of the cup-wall has been changed into iron peroxide, and is not 

 recognizable. The spicules of the stem are elongate and irregular in form. 



Distribution. Upper Chalk : South of England {coll. Bowerbank and Toul. Smith). 



Genus PLEUROSTOMA, Boem. 1840, emend. Zitt. 1877. 

 Pleurostoma radiatum, Bcemer. 



1840. Pleurostoma radiatum, Roemer, Nordd. Kreide, p. 5, t. 1. f. 11. 



1877. Pleurostoma radiatum, Zitt. Studien, I Ab. p. 48 ; Neues Jahrbuch, p. 358. 



The only specimen in the collection referable to this species is an elongated, 

 geniculate, much compressed stem 100 mm. in length, 14 mm. in width, and 

 3-5 mm. in thickness. At the basal end are several lateral root-like processes ; 

 the summit is imperfect. The walls of this hollow stem are about '75 mm. in 

 thickness. On both the lateral edges of the stem there are at irregular intervals 

 circular or ovate apertures from 2 to 3 mm. in width, which open into the central 

 hollow. The outer surface of the wall is provided with numerous closely set circular 

 apertures '35 mm. in width, and about the same distance apart, and without definite 

 arrangement. The spicular mesh has been replaced by iron peroxide. 



Distribution. Upper Chalk : South of England {coll. T. Smith). 



