internal Structure of the Magnesian Limestone, 119 



Bivalves. 



1. Producia aniiquata, Min. Con. t. 317. fig. 1. 5. 6 — This fossil (so common in the mountain 

 limestone) occurs rarely in the compact limestone over the marl, slate at Midderid^e* 

 P. calva, a. ^. Min. Con. t. 560. fig. 2— 6.— Occurs abundantly at Humbleton, in the com- 

 pact beds of Midderidge ; in the dark beds near Nosterfield, &c. &c. f 

 P. horrida, Min. Con. t. 319. fig. 1 — Humbleton ; Whitley quarry ; Northumberland • 



yellow limestone, Derbyshire. 

 P. spinosa, Min. Con. t. 69. fig. 2. — Humbleton quarries, &c. 

 A species of Producta, probably difl'ering from all the preceding, was found by Mr. Phillips 

 near Ferry-Bridge J. 



2. Spirifer undulatus, Min. Con. t. 562. fig. 1. — Compact limestone, Midderidge and Hum- 

 bleton, &c. 



To the preceding list must be added two, or perhaps more, species of small shells of the o-enus 

 Spirifer, chiefly derived from Humbleton and Tunstal Hill. One {S. multiplicatus)\\a.% many plaits 

 in front, and shows the internal structure peculiar to the genus. Another (S'. minutus) is very 

 minute, but is well characterized. Two or three other species of small shells are doubtful and 

 may perhaps belong to the genus Terebratula. 



3. Terebratula. — Shells of this genus (generally of a small size) occur in many parts of the 

 formation, particularly at Tunstal Hill and Humbleton. Of these there appear to be not less 

 than five or six distinct species. Some are smooth; others plaited or ribbed. Some are flat • 

 others spheroidal. Some are broad ; others oblong. A beautiful, small, smooth species forms 

 nearly the whole mass of some rocks near Dalton-le-Dale. 



4. Aximis obscicrus, Min. Con. t. 314. — Many casts of this species occur at Wentbridge Hill 

 in the lower beds of yellow limestone, and in the same part of the series at Garforth clilf. It is 

 found in a much more perfect form in the lower beds of Stubbs Hill. Casts of this genus are 

 found also south of Black Rocks, on the Durham coast. 



5. uirca tumida, Min. Con. t. 474. fig. 3.—- Tunstal Hill and Humbleton. 



6. Cucullcea sulcata (S. N.), generally very imperfect, and in casts; which, however, some- 

 times show the nature of the hinge : transverse dimension about li inch ; on one specimen a 

 small part of the shell is preserved, which is deeply striated. Humbleton, &c. 



7. Avicula gri/phcEoides (S. N.). — This small species (which in external character resembles 

 a gryphite), abounds at Humbleton. The convex valve has many very small slightly tuberculated 

 ribs. The other valve is discoid and nearly smooth. 



There are some imperfect specimens of another striated species which resembles a Gervillia. 



8. Ostrea. — Casts of a small flat species occur at Whitley quarry, Northumberland. 



9. Astarte (?). — Casts of a beautiful shell about half an inch in length, marked with con- 

 centric striee, and apparently of this genus, abound in some of the beds of Whitley quarry. 



10. Modiola acuminata (S. N.). — A very small species found in very great abundance in 

 some shelly beds south of Black Rocks, Durham. A larger species, length half an inch, occurs 

 in the upper thin-bedded limestone at Cold Hill, a few miles east of Aberford. Casts of another 

 very small species of Modiola, in form much less acuminated than the preceding, occur at Hum. 

 bleton. Found also by Mr. Phillips at Hawthorn Hive. 



* See p. 77, f See p. 108. % See Annals of Philosophy, Dec. 1828, 



