PEEONELLA.— TEEMACTSTIA. 171 



Pekonella ocellata, Hinde. (Plate XXXIII. figs. 9, 9 «, 9 i, 9 c.) 



Sponges mostly simple, subcylindrical stems from 4 to 6'5 mm. in thickness, and 

 from 15 to 22 mm. in height, apparently growing from a slightly expanded base. 

 In some cases one or two small lateral buds spring from the surface of the main stem. 

 The summits are truncate or slightly rounded, and the cloacal aperture is about 

 1'5 mm. in width. The outer surface is smooth, and is apparently furnished with a 

 dermal layer, perforated by numerous irregularly disposed circular apertures "4 mm. 

 in width, generally subdivided by cross bars of fibre. Very minute pores occur in 

 the interspaces between the larger apertures. The fibres, seen in a transparent 

 section, are about T4 mm. in thickness. Unfortunately no minute structure is 

 preserved. 



This species is readily distinguished by its mode of growth and the characters of 

 the outer surface. 



Distribution. Upper Chalk : Maestricht. 



Genus TEEMACYSTIA, Hinde, n. g. 



Syn. Verticillites, auct. (non Defrance) ; Verticillopora, Mantell, Sharpe (non Blainville) ; 

 Ceriopora, pars, Goldf. ; Thalamopora, F. A. Roemer, Mich., Pomel, Simonowitsch, 

 Reuss, Steiiim., Dunik. ; Discoelia, Jjonol; Sphceroccelia, Stemm.., Dunik.; Barroisia, 

 Steinm., Dunik.; Veriicil/occelia, pars, From. 



Sponges simple, or growing in bushy masses from a common base ; the stems 

 occasionally give off lateral branches. Individual forms are cylindrical, inverted- 

 conical, or club-shaped, and are composed of a series of cylindrical, subspherical, or 

 cyst-like hollow segments superimposed over each other. The segments are mostly 

 connected together by a central aperture in the roof of each, and by a more or less 

 developed axial tube usually perforated laterally with large apertures opening intb 

 the different segments. The exterior wall of the sponge and the segmental divisions 

 are formed by a single layer of anastomosing fibres, penetrated by numerous minute 

 canals. 



The skeletal fibres are composed of minute filiform three-rayed spicules in close 

 contact with each other, and disposed generally parallel to the axis of the fibre. 

 The basal ray of these spicules is generally so minute that it can scarcely be 

 detected in microscopic sections when the spicules are closely intermingled. Besides 

 these filiform spicules, the outer surface of the sponge is furnished with a dermal 

 layer of relatively large three- and four-rayed spicules. Possibly uniaxial spicules 

 may also occur in the fibres, though what appear as such in thin sections are, in my 

 opinion, portions of three-rayed spicules. 



I propose this genus to include a group of well-known sponges, hitherto referred 

 to several genera, but which are naturally connected by their segmental growth, 



z2 



