VENTETCULITES. Ill 



in this latter species have a rectangular arrangement, and the wall is three times as 

 thick as in V. convol ictus. 



This species appears to be not uncommon in the Kentish Chalk. 



Distribution. Upper Chalk : Gravesend, Broadstairs, Kent. 



Ventriculites poculum, Zittel, MS. 

 Distribution. Upper Chalk : Libyan Desert {Zitt. coll.). 



Ventriculites decureens, Toulm. Smith. 



1848. Ventriculites decurrens, T. Smith, Ann. & Mag. Nat. Hist. 2ncl ser. vol. i. p. 215, 



t. 13. f. 8. 

 1848. Ventriculites decurrens, var. tenuiplicatus, T. Smith, ibid. p. 215, 1. 13. f. 9. 

 1848. Ventriculites cavatus, T. Smith, ibid. p. 212, 1. 13. f. 5. 

 1822. Ventriculites radiatus, Mantell, pars, Foss. South Downs, t. 13. f. 4. 

 1878. Ventriculites radiatus, Qucnst. pars, Petref. Bd. 5, t. 13G. f. 23. 



Sponges varying in form, from subcylindrical to open funnel-shaped, gradually 

 tapering below to a slender cylindrical stem with branching roots. Small examples 

 measure 65 mm. in length by 23 in diameter, whilst a large specimen, without the 

 slender stem, is 120 mm. in height and of an equal width at the summit. 



The outer surface of the sponge is formed by robust vertical or oblique ridges, 

 which occasionally bifurcate, but are rarely connected by lateral extensions. These 

 ridges are 2 mm. in thickness, and the intervening furrows about '75 mm. in width. 

 The interior surface exhibits circular apertures. The entire thickness of the sponge- 

 wall is 5 mm. The dermal layer of the exterior ridges of the wall is penetrated by 

 numerous minute circular pores, and minute spinous processes project outwards 

 from its surface. The spicular mesh of the interior appears to be of an irregular 

 character. 



This species is also abundant. It somewhat approaches to V. radiatus in the 

 disposition of the ridges and furrows of the outer portion of the wall, but its mode 

 of growth readily distinguishes it from that species. The V. cavatus, T. Smith, 

 which is founded on a mere fragment of the wall of a sponge, appears to me to 

 belong to the present species. 



Listyibution. Upper Chalk : South of England ; Bridgwick ; Monckton-Bassett, 

 Wilts {coll. T. Smith and Mantell). 



Ventriculites mammillaeis, Toulm. Smith. 



1848. Ventriculites mammillaris, T. Smith, Ann. & Mag. Nat. Hist. 2nd ser. vol. i. p. 213, 



1. 13. f. 7, 14. 

 1822. Ventriculites radiatus, Mantell, p. p. Foss. South Downs, t. 13. f. 2, 3, 5. 



Sponges either elongated, narrow, funnel-shaped, or somewhat depressed, open 



