242 M. K. A. Zittel on Fossil Lithistidce. 



Siphonla, Park. (Cretaceous). Fig-shaped or pyriform, stalked. Central 

 cavity wide, with ostia of bent radial canals. There are also canals 

 running obliquely from within outwards. 



Jerea, Lamx. (Cretaceous). Like Sijihonia, but with a bimdle of vertical 

 tubes, the ostia of which open at the vei'tex. 



Nelumbia, Pom. (Cretaceous). Clavate. Vertex with the ostia of short 

 vertical tubes. .Sides with impressions in which canals open. 



?Mar(/inospanf/ia, D'Orb. (Cretaceous). Cup-shaped, stalked. Wall 

 traversed by vertical tubes. 



Polyjerea, From. (Cretaceous). Tufted. All individuals traversed by 

 tubular canals. Surface coated with a siliceous skin consisting of 

 small branched lithistid corpuscles. 



Astrocladia, Zitt. (Cretaceous). Simple or branched, cylindrical, massive. 

 Oscula scattered, in connexion with tubular canals, 



Caly^mnatinUj Zitt. (Cretaceous). Branched or simple. Tlie individuals 

 trochiform, with simple stomachal cavity. Surface rough, com- 

 pletely coated with a siliceous skin in which forked anchors lie. 



Thecosiphonia, Zitt. (Cretaceous). Simple or polyzoic. Individuals 

 trochiform. Vei'tex with an impressed pit, in which are the 

 openings of vertical tubes. Base and a part of the sides coated with 

 siliceous skin. 



Turom'a, Mich. (Cretaceous). Irregular, nodular. Upper surface convex 

 or conical, rough, with longitudinal furrows. In the interior scat- 

 tered vertical tubes. Base with a siliceous skin, in which are forked 

 anchors. 



c. Skeletal elements quadriradiate, strongly branched at 

 tlie ends. In the surface short-shafted forked anchors with 

 curved prongs, or with lobate or round, short-stalked siliceous 

 disks. 



Theonella, Gray (Cretaceous and Recent). Cup-shaped. Outer surface 

 porous ; inner surface with numerous not prominent oscula. Anchors 

 of the surface with curved forked prongs. 



Discodertm'a, Bocage (Cretaceous and Recent), Cup-shaped. Surface 

 with entire-mai'gined rounded siliceous disks. 



Kaliapsis, Bow. (Recent). Incrusting, thin, without oscula. Siu-face 

 with toothed, multilobate, short-stalked, siliceous disks, 



Hhacodiscida , Zitt, (Cretaceous and Recent), Clavate, nodular, cylindri- 

 cal or cup-shaped. Surface with lobate, short-stallted, siliceous 

 disks. 



Rhagadinia, Zitt. (Cretaceous). Basin-shaped or laminar. Surface with 

 fuiTow-canals. Covering layer consisting of lobate, short-stalked, 

 siliceous disks and baciUar spicules. 



d. Skeletal elements large, quadriradiate, knobby, with the 

 ends eitlier very slightly branched or merely thickened. 



PUnthosella, Zitt, (Cretaceous). Globular or nodular. Surface wth 

 large, tile-Uke, entire-margined or lobate siliceous disks. 



Spoil f/odiscHS, Zitt. (Cretaceous). Disciform. Upper surface with ra- 

 diating ribs. Caual-sj'stem wanting". 



In this classification, with a few exceptions, only such genera 

 are accepted as I have myself examined microscopically. I 

 have left out of consideration a number of the genera of 



