FROM THE INFERIOR OOLITE. 491 



1849. 0. Knorrii, D'Orb. Prodr. vol. i. p. 257. 



1857. 0. Knorrii, Oppel, Juraform. p. 493. 



1858. 0. Knorrii, Querist. Jura, t. 66. figs. 37-42. 

 1864. 0. Knorrii, Seeb. Haun. Jur. p. 93. 



1869. 0. Knorrii, Brauns, Mittl. Jur. p. 278. 



1871. 0. Knorrii, Terq. & Jourdy, Mem. Soc. Geol. France, ser. 2, 

 vol. xix. p. 133. 



This little shell differs from Ostrea cosiata, Sow., by being much 

 more finely and regularly rayed. The rays are more rounded and 

 simpler, and the shell is, as a rule, more convex. 



It occurs abundantly in the Inferior Oolite of Bradford Abbas 

 and in the Fuller's Earth near Frome. There are also specimens 

 in the British Museum from the Fuller's Earth of Box, and 

 Yon Seebach states that Mr. Day found it in the same beds near 

 Bridport. 



Those from the Inferior Oolite seem to attain a larger size than 

 the others ; but, as pointed out by Oppel, Terquem, &c, the number 

 and nature of the ribs and its pear-like form render it easily sepa- 

 rable from Sowerby's shell, with which Goldfuss has confounded 

 it. Dr. Brauns wrongly identifies it with 0. subrugulosa, Morr. & 

 Lye, from which it is very distinct. 



The area of attachment is usually small, but occasionally forms 

 a fiat surface over the upper half of the shell, and one of my spe- 

 cimens has taken the marks of a Pecten over the greatest portion 

 of its exterior. The right valve is smooth and flat in our English 

 examples ; and this, which agrees with Quenstedt's definition, 

 throws the only doubt over the correctness of its identification, as 

 Zieten's figures give similar ribs on both valves. As, however, he 

 quotes it from the Fuller's Earth, it may be supposed either that 

 his was an exceptional or aged example, or that there is a mistake 

 in the drawing. This is the more likely, because in 0. costata, 

 Sow., the flat valve is generally as smooth as he describes it, but 

 in aged examples it is sometimes as strongly ribbed as the other. 

 Moreover, Homer says that in this species it is generally smooth, 

 but sometimes rayed ; and Knorr's excellent and characteristic figure 

 also gives it ribbed. 



Note on Ostrea costata. 



An inspection of Sowerby's original specimens in the British 

 Museum can leave no doubt of the correctness of Morris & Lycett's 

 determination, the roundness of the ribs to which he refers being 

 very slight, and probably due to the youth of his Ancliff specimens. 

 Larger fossils in the Lycett collection are extremely like miniatures 

 of O. Marshii, Sow., and might well be imagined to be the young of 

 that species, were it not that in its early stage it is stated by Morris 

 and Lycett to be almost ribless and akin to 0. sulcifera, Phill. 

 Again, intermediate between them comes 0. solitaria, chiefly from 

 the Corallian, though fossils from the Inferior Oolite of Yorkshire 

 are referred to it in the London museums. It seems to have a 

 definite shape and facies of its own, besides being nearly confined 



