EUBEOCHTTS.— PEOTOSPONGIA. 129 



Genus EUBROCHUS, Sollas, 1876. 



EUBROCHDS CLAUSUS, Sollas. 



1876. Eubrochus clausus, Sollas, Geol. Mag. vol. iii. n. s. p. 398, t. 14. 



1877. Eubrochus , Zitt, Studien, I Ab. p. 46. 



Small, inverted conical sponges, with truncated or rounded summits. The lateral 

 surfaces are covered with continuous fine linear grooves, which decussate with each 

 other in such a manner as to form small quadrate or oblong interspaces, the sides of 

 which are about 'S mm. in length. The summit of the sponge is also covered with 

 a similar lattice-work, but the lines forming it do not decussate as on the sides, but 

 are disposed at right angles to each other. The characters of the interior structure 

 of the sponge are too imperfectly preserved for satisfactory determination. Prof, 

 Sollas has figured fragments of spicular mesh {loc. cit. figs. 4, 5) with which, he 

 states, the interior of the sponge was filled ; but after a careful examination of the 

 type specimens in the collections of the Woodwardian Museum at Cambridge and of 

 the Jermyn-Street Museum, I could only detect in the sections of the interior a few 

 broken-up fragments of hexactinellid spicules, which were altogether insufficient to 

 give me a clue to the original structure of the interior skeleton. 



Distribution. Cambridge Green Sand : Cambridge [coll. Tracy). 



Genus PEOTOSPONGIA, Salter, 1864. 



Peotospongia fenesteata, Salter. (Plate XXVIII. fig. 2.) 



1864. Protospongia fenestrata, Salt. Quart. Journ. Geol. Soc. vol. xx. p. 238, 1. 13. f. 12 a, b. 

 1871. Protospongia fenestrata, Hicks, Quart. Journ. Geol. Soc. vol. xxvii. t. 16. f. 20. 

 1877. Protospongia fenestrata, Zitt. Studien, I Ab. p. 45; Neues Jalirbuch, p. 354. 

 1880. Protospongia fenestrata, Ferd. Roemer, Leth. Geogn. 1 Th. p. 316, f. 59. 

 1880. Protospongia fenestrata, Sollas, Quart. Journ. Geol. Soc. vol. xxxvi. p. 364, f. 1. 



Form of sponge unknown ; the portions preserved consist either of detached 

 spicules or fragments of a delicate spicular framework formed of a single layer of 

 four-rayed spicules of various dimensions. The larger spicules are arranged so as to 

 form regular squares, which are divided by smaller spicules into smaller squares, and 

 these are again subdivided ; so that the surface of a fairly complete specimen 

 resembles minute lattice-work. It is probable that a delicate spicular membrane 

 connected the entire framework together, as there is in many specimens a thin film 

 of ii-on pyrites between the interspaces of the lattice-work ; and as the larger spicules 

 are now in the condition of iron pyrites, this film of the same material may represent 

 a spicular membrane whose minute rays have been indistinguishably merged 

 together. 



The not infrequent occurrence of portions of the spicular framework with the 



s 



