M. K. A, Zittel on Fossil Lithistidce. 133 



ing excrescences. Similar furcate anchors beset with nodose 

 warts also occur in some recent Lithistidge (such as Coral- 

 listes nolitangere^ fig. 7, c.) 



A remarkable modification of the furcate anchor with arms 

 standing perpendicular to the shaft is to be observed in the 

 genus Theonella. Here the shaft is reduced to a short, 

 pointed style, the three arms are compressed from above, 

 curved, and divided at the ends into two short branches (see 

 Bowerbank, I. c. fig. 306, and Proc. Zool. Soc. 1869, pi. v. 

 figs. 8, 9). In the fossil genus Rhagadima, and in an unde- 

 scribed recent Rhacodiscula kindly communicated to me by 

 Mr. Carter, the shaft is still shorter, and the very broad com- 

 pressed arms divide into two, three, or more irregular lobes. 

 In the centre there is a very short quadriradiate axial cross. 

 . Surface-spicules of this kind are figured in my monograph of 

 CoeloptycUum (Taf. vii. figs. 25-27, 29, 30). Carter has de- 

 scribed similar forms from the Greensand of Haldon, under 

 the name of Dactyhcaly cites Vicaryi *. If the shaft be re- 

 duced to a minute stylet, and the rays of the axial canal become 

 still shorter, the depressed arms of the furcate anchor broader, 

 and their lobate branches more numerous, structures are pro- 

 duced such as the short-stalked many-lobed siliceous disks 

 represented in my monograph of Coeloptychium (Taf. vii. 

 figs. 36, 37), or those figured by O. Schmidt [l. c. Taf. iii. 

 fig. 8) as Corallistes ])ohj discus^ Schm. (not Bocage), by 

 Bowerbank (Mon. Brit. Sp. figs. 104-106) as " foliato-peltate 

 spicules," and by Carter (?. c. pi. vii. figs. 3, 4) as Dacty- 

 localycites polydiscus from the Greensand of Haldon. Similar 

 minute disks occur in Kaliapsis. 



Close to these come the sometimes circular, sometimes oval 

 siliceous disks of Discodermia polydiscus, Bocage (see Bower- 

 bank, Proc. Zool. Soc. 1869, pi. vi. figs. 10, 11), in which 

 there are in the centre a minute conical stylet and a short 

 quadriradiate axial cross. Carter (/. c. pi. vii. fig. 5) has 

 also found the same disks fossil ; and with these may proba- 

 bly be ranged the large irregular and angular siliceous plates 

 of the fossil genus Plinthosella. 



In the neighbourhood of Discodermia we must possibly also 

 place those elegant siliceous disks with highly-developed 

 and repeatedly divided radial canals, and perforated at the 

 margin, of which I have already figured several specimens 

 {Coeloptychium^ Taf. vi. figs. 32-35). Similar disks are de- 

 scribed by Carter from the Greensand of Haldon {I. c. pi. ix. 

 figs. 40-42). 



• Ann. & Mag. Nat. Hist. ser. 4, yoI. vii. (1871) pi. vii. figs. 1, 2, 



