T. 0. Bosworfh— Zones of the Lower Chalk. 417 



LAMEIXinUANCHIATA. 



*J)imydion Nils.wni ( = FHcatula sigillina) (attached 



to test of Holastfr) ... . . ... ... 2 



Ontrea vesiciUuris ... ... ... ... very numerous 



*()strcajilala... ... ... ... ... ,, ,, 



Feci en Heaver i ... ... ... ... ... 7 



Inoceranius R\}. .. ... ... ... ... 3 



Spondylm latns ... ... ... ... ... 1 



*2'e/Yrf'o, sp. uov. (P) a group 



POLYZOA. 



*Froboiictna ... ... ... ... ... ... 1 



*Stomatopora (?) numerous 



Annelida. 

 * Serpula umhonata ... ... ... ... ... 1 



Note. — Those marked with an asterisk (*•'') have not been 

 previously recorded from the " Chalk above the Burwell Rock " 

 of Cambridgenliire and Suffolk. 



There are several points of interest about this fauna. 



(1) The specimens of Discoidea are of very unusual size (base 

 2^ inches in diameter). I can find no recoi-d of any so large as this. 



(2) Tlie tubes of Teredo are very fine and probably belong to 

 a new species. 



(3) The absence of Bhyiichoiiella, although abundant in the zone of 

 B. jileua just above. 



(4) No specimen of Holaster subglohosus has occurred. 



(5) B. trecensis is unusually abundant, the test being thin, and 

 taken with the rest of the fauna suggesting deeper water. 



(6) Ostrea filata here includes two forms previously supposed 

 distinct. The left valves are very abundant, occurring attached to 

 specimens of Holaster. They have liitherto been erroneously ascribed 

 to Ostrea vesiculosa. An excellent figure may be seen in Dr. S. P. 

 Woodward's paper (Geol. Mag., 1864, p. 114, Plate V). But they 

 have little I'eserablance to the original Ostrea vesiculosa from the 

 Upper Greensand of Warminster described and figured in Sowerby's 

 Mineral Conchology (v(d. iv, pi. 369) as Gryphcea vesiculosa, and 

 afterwards found to be an Ostrea. The right valves have liitherto 

 been referred to as Avicula filata, a species described by Etlieridge. 

 The type-specimen and three others, all from the Burwell Hock of 

 Burwell, are in tlie Sedgwick Museum. I find it quite common in 

 the Burwell Rock at Full)0urn. 



In the monograph of the " Cretaceous Lamellibranchs of Eng- 

 land " Mr. Henry Woods makes the following remark on this 

 species (footnote, p. 61, vol. ii, part 2): "I am unable to accept 

 the generic position assigned to this species by Etheridge ; it may 

 be an Ostrea." 



Though the left valves (^Ostrea vesiculosa) are so plentiful I have 

 only found two right valves (the so-called Avicula filata). But one 

 of these is in position attached to the left valve of the so-called 

 Ostrea vesiculosa, which is itself along with several other left valves 

 attached to a specimen oi Holaster trecensis. 



Mr. Woods has closely examined these specimens, and is satisfied 

 that Avicula filata and the so-called Ostrea vesiculosa are right and 

 left valves of the same shell. 



nFOADK V. TOL. III. NO. IX. 27 



