482 



MOLLUSCA 



PHYLUM VI 



unequal, slightly excavated adductor scars, correspouding to two broad niyophores in 

 the upper valve. Middle and Upper Cretace- 

 ous ; Europe and Texas. 



Subgenera : LcqKirousia Bayle. The smooth 

 bands correspond internally to two prominent 

 tubercles. Synodontitcs Pirona. Has the two 

 teeth of the upper valve fused. 



Sphaerulites Delam. {RacUolites, Birostrites 

 Lam. ; Jodamia Defr. ; Bipilidia. 1 Agria 

 Math.) (Figs. 779- 



781). Externally 

 like Radiolites, but 

 without the two 

 bands; valves with 

 a re-entrant sinus 

 between the teeth, 

 which fit into sepa- 

 rate pits {d, d'), 

 usually joined by a 

 y^ith the 



Fic. 780. 



Pifi. 781. 



Sphaemlites foliaeeiis Lam. Carentonian ; lie 

 d'Aix, Charente. ^-1, Sinus of the liin^e. a, a'. 



riclge 



Portion of the outer shell layer Anterior and posterior adductor scans ; (/, d', 

 of the lower valve of a Sjihacru- Anterior and posterior grooved sockets for the 

 lites or Iladiolites showing the processes of the upper valve ; ;c, x', Empty spaces 



of the ligament pits ; y, Cavity at the inner end 

 of the sinus. 2/3 (after Goldfuss). 



innor imro-hi of '^'S® hollow prisms. Cretace- 

 mnei margin 01 ^^^^ . ^^^^^ Oargano, Italy, i/j. 



the sinus ; the two 



dej)ressions (Fig. 781, x, x) next the sinus were shown by Petho to have been the 



seat of a ligamentary connection lietween the valves ; the adductor scars («, a) resemble 



those of Radiolites. Widely distributed in the Middle and Upper Cretaceous. 



The supposed genera Dipilidia, Birostrites and Jodamia are based on internal 



moulds of Radiolites. The visible submersion of the ligament in some Radiolites 



enables us to understand how the stages shown by Hifinmtes have arisen. 



Family 14. Hippuritidae Gray. 



Shell substance of two layers, the external j^orous, grooved and punctate; the inner 

 lacunary and ■prismatic ; exterior with sutures corresponding to an " anal " and 

 '' branchial " inflection, and sometimes with a, ligamentary suture ; clithrum formed of 

 tiw processes in the free valve, the adductors attached to myophores ; fixed valve with one 

 thin laminar process ; the adductor scars excavated, the anterior adductor duplex, forming 

 distinct scars. Cretaceous. 



Hippxhrites Lam. (Figs. 782-786). Lower valve cylindro-conic, sometimes a metre 

 in length, attached by the apex, smooth or longitudinally ribbed, with three furrows 

 bounding two " columns," or columnar areas, extending from the ajjex to the upper 

 margin {A, B, G). Upper valve depressed, conic, with sub-central umbo, usually with 

 two round or oval foramina ; outer surface showing pores, the apertures of short canals 

 which join larger canals radiating from the beak. The thick outer layer of the lower 

 valve is usually brown -coloured and made up of thin horizontal strata, which are in 

 turn composed of small vertical prisms. The white inner layer is porcellanous, and 

 sometimes contains vacant spaces in the lower part of the shell. Three prominent 

 folds are present, on the inner side of the shell, formed l;)y the inbending of both 

 layers of shell, and corresponding to the external grooves {A, B, (J). Of these the 

 anterior {A) i§ longer and thinner than the others, which are thickened at the internal 

 end and carry a small tubercle above. In the two subgenera, Orbignyia Woodward 

 {H. biloculus Lam.), and Batolites Montibrt {H. organisans Lap.), the anterior sinus 

 disappears entirely. In Pironaea Menegh., a number of accessory folds apj^ear behind 

 the two columns. According to Douville, the two posterior columns are homologous 



