VIl] BORINGS IN SHELLS. 127 



" leathery sheet of tough gelatinous material," or in " the skeins 

 of delicate white filaments" which make up the travertine 

 deposits. 



Under the head of Cyanophyceae, mention should be made of 

 the recent genus Hyella^, which occurs as a perforating or boring 

 alga in the calcareous shells of molluscs. On dissolving the 

 carbonate of lime of shells perforated by this alga, the latter 

 is isolated and appears to consist of rows of small cells, with 

 possibly some sporangia containing spores. Other boring algae 

 have been recorded among the Chlorophyceae, and recently a 

 member of the Rhodophyceae^ has been found living in the 

 substance of calcareous shells. Such examples are worthy of 

 note in view of the not infrequent occurrence of fossil corals, 

 shells and fish-scales, which have evidently been bored by an 

 organism resembling in form and manner of occurrence these 

 recent algal borers. 



The occurrence of small ramifying tubes in recent and 

 fossil corals, fish-scales, and bones was long ago pointed out by 

 Quekett^ Kolliker^, Rose^ and other writers^. These narrow 

 tubular cavities have generally been attributed to the boring 

 action of some parasitic organism, either a fungus or an alga. 

 In 1876 Duncan published two important papers'' dealing with 

 the occurrence of such tubes in recent corals, as well as in 

 the calcareous skeleton of Calceolina, Ooniophyllum and other 

 Palaeozoic, Mesozoic and Tertiary species of corals. This writer 

 attributed the formation of the cavities in the case of the fossil 

 species to the action of a fungus which he named Palaeachyla 

 perforans, and considered as very nearly related to Achy la 

 penetrans found in the " dense sclerenchyma " of recent corals. 

 In fig. 27 A. is reproduced one of the drawings given by Rose " 



1 Bornet and Flahault (892) PI. xi. « Batters (92). 



3 Qnekett (54), fig. 78. ^ Kolliker (59) and (59*) ; good figures in the 



latter paper. 



6 liose (55), PI. I. 



" For other references vide Bornet and Flahault (89-). 



7 Duncan (76) and (762). 



8 Similar borings are figured by Kdlliker (69*), PI. xvi. 1-4, .u ,t n> ,ilo of 

 Beryx ornatus from the Chalk. 



