78 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Dec. 18, 



The osculiform pits are grouped sometimes at the end of one of the 

 wrinkled depressions above described ; sometimes they are collected 

 in sieve-like patches, or two or three may be noticed at the bottom 

 of a wider-mouthed pit, while occasionally they are terminal, and 

 frequently dispersed. It may be noticed that in the same specimen 

 these pits occur of very various sizes, and that the striated grooves 

 of their margins are never arranged in any multiple of four — an 

 argument, if arguments are needed, against the alcyonioid origin of 

 these forms. 



(iii.) The puncta are minute pore-like markings, which appear in 

 the greensand specimens as mere specks of a different nature from the 

 rest of the fossil ; but in the gault coprolites they are the distinctly 

 open terminations of fine canals. 



(iv.) Contraction- cracks are evident on the surfaces of many 

 specimens, generally filled in with lighter-coloured material. In the 

 coprolites from the Gault the oscula, puncta, canals, cracks, and 

 other cavities are either empty or filled with loose clay; in those 

 from the Greensand all these cavities are infiltrated with phosphatized 

 chalk-marl, containing green grains and sometimes diffused glau- 

 conite. Since these infiltrated coprolites of the Greensand are de- 

 rived from those of the Gault. which are not infiltrated, this filling-in 

 must have taken place after the greensand fossils were washed out 

 of their matrix. 



Smooth surfaces of attachment are to be seen on some specimens ; 

 and in rare cases the shell on which they grew remains adherent to 

 them. 



General Appearances under the Microscope. — Thin sections exa- 

 mined under the microscope vary from colourless to yellowish- 

 brown when transparent, but sometimes they are almost opaque 

 from included earthy matter. Granular patches of a deep red colour 

 are sometimes scattered throughout the fighter-coloured portions. 

 Spicules occur in many sections, presenting some of the most cha- 

 racteristic forms of sponge-spicules, as for example, hexaradiate, tri- 

 radiate, hamate, sinuate, and connecting forms. These spicules 

 are frequently grouped together in a manner which would seem to 

 indicate that they cannot have been washed in from the sea-bed 

 during fossilization. Globular bodies -^- 6 " in diameter are numerous ; 

 they seem to be gemmules. Polycystina and Xanthklia occur in 

 some sections. With polarized light the sections appear distinctly 

 cryptocrystalline, presenting an appearance very nearly resembling 

 that of chalk flints when examined in the same way. A very 

 curious phenomenon may be alluded to here. A number of small 

 circles may be seen in some sections, each of which is marked by a 

 black cross, the arms of which radiate from the centre to the cir- 

 cumference. On turning the analyzer the cross revolves and, when 

 he analyzer has been turned round 90°, is replaced by a complemen- 

 tarity illuminated cross. The explanation of these appearances seems 

 to be as follows : small Olobigerina-sheils and other similar spaces 

 occur in the coprolite, into which the crystalline apatite which was 

 diffused throughout the fossil has penetrated and crystallized inwards 



