TRANSACTIONS OF SECTION C. 587 



silicified. By treating the flints with dilute acid, a siliceous sediment remains, 

 consisting of silicified tests of foraminifera, valves of entomostraea and erinoidal 

 network, siliceous and glaucouitic casts of foraminifera, and sponge-spicules. 

 Amongst the siliceous casts of foraminifera is a dumbbell-shaped form, derived 

 from two chambers of a Nodosaria, and mistaken by Zittel for a sponge-spicule. 

 The sponge-spicules are snow-white and opaque by reflected light, but when 

 moimted in Canada balsam so transparent as to be nearly invisible. They have 

 become crypto-crystalline, give colours with polarised light, and have correspond- 

 ingly acquired a higher refractive index than they possessed in the fresh state 

 (Sollas, ' Ann. and Mag. Nat. Hist.' 1877, vol. xix. p. iiO). They are eroded super- 

 ficially, and sometimes covered with little hemispherical pits ; occasionally dendrites 

 of iron pyrites are seen shooting through their substance, the flrst stage of a replace- 

 ment which is found completed in spicules from other deposits. 



The spicules belong cliiefly to Hexactinellid and Tetractinellid sponges. Of the 

 latter forms Lithistids are frequent ; they resemble the recent forms Corallistes mi' 

 crotuberculatus, Lyidium torquilla, Discodermia polydiscus, Rhacodiscula astei'oides, 

 and Kaliapsis cidaris ; and are allied to the cretaceous genera described by Zittel 

 iinder the names Pachinion scriptmn, Scytalia turbinata, Dorydermia dichotoma, 

 Callopegma acaule, and Ragadinia rirnosa. The forms resembling Kaliapsis may 

 be termed Coinpsapsis cretacea. The depth at which the living Lithistids most 

 nearly related to the fossil ones have been found, varies from 74 to 375 fathoms. 



Of other Tetractinellids there are stellate globides referable to Tethya, and 

 scarcely distinguishable from those of Tethya lyncurium ; these may be knowTi as 

 Tethylites cretaceus, a genus not in any way related to Zittel's Tethyopsis, as that 

 is placed by him with Tetilla cranium. Calthrop-like spicules referable to Carter's 

 Dercitites Haldonensis are common, also others probably related to Zittel's Pachas- 

 trella pnmcva. Tuberculated globules, similar to the characteristic globules of 

 Pachnstrella geodoides, Carter, occur. This li-ving species was brought up from a 

 depth of 292 fathoms, near St. Vincent's. 



Ordinary geodid globules of various sizes are exceedingly common in various 

 stages of decay, similar to those which the author has produced artificially in 

 recent sponge-spicules by the action of caustic potash. "With the globules were 

 associated the usual geodid anchors, grapnels, and acerate spicules. Many are of 

 the same forms as Carter's Geodites Haldonetms, and find tlieir nearest ally in the 

 existing Geodia McAndretm, which has been dredged from 100 to 270 fathoms. 



A club-shaped spicule, i.e. generally conical, rounded at the ends, and tubercu- 

 lated all over, ^'^^-inch long, and j~ broad where largest, is not unfrequent ; it is quite 

 unlike any existing spicule, and may be provisionally termed Phopaloconus cretaceus. 



Many other forms not mentioned here occur plentifidly, and the nimiber of 

 difierent species found in the same flint is remarkable, but in this connection it may 

 be remembered that Carter has described no less than seven entirely difierent 

 species of sponge growing together on a thin fragment of Lophohelia prolifera, not 

 quite two square inches in extent. 



TUESDAY, AUGUST 31. 

 The following Reports and Papers were read : — 



1. Report on the Tertiary (Miocene'), Flora of the Basalt of the North of 

 Ireland. — See Reports, p. 107. 



2. Report on the Erratic BlocJcs of England, Wales, and Ireland. 



See Reports, p. 110, 



