J. Wd ackson—Brachiopod Morphology. sli 
below the surface of the sea, and to have given rise to the amount of 
combined water found in the different samples of sandstone, we can 
arrive at the comparative depth of the various points in the basin 
where analyses have been made. 
A section through the St. Bees basin from Calder Abbey to St. Bees 
will thus show a maximum depth at a point almost midway between 
St. Bees and Whinscales, the depth decreasing north and south. 
Similarly, in the northern basin the maximum depth is attained 
a little north of West Newton, and decreases more rapidly to the 
south than to the north. Thus both basins were steeper at their 
southern extremity than at their northern. 
The depth of the basin at Maryport was not very great ; in fact, we 
have evidence in the form of ripple-marks of littoral conditions at this 
place. 
VI. —Bnracuiopop MorrHotocy: Norrs ann Comments on Dr. J. 
Auttan THomson’s PAreErs. 
By J. WILFRID JACKSON, F.G.S., Assistant Keeper, Manchester Museum. 
)\ROM a long and careful study of the Brachiopoda I am led to 
offer some observations upon the two recently published papers 
by Dr. J. Allan Thomson which have appeared in this Magazine.} 
In the case of Dallina I cannot agree with Dr. Thomson regarding 
the type of folding. He considers D. septigera (the genotype) and 
D. raphaelis as dorsally biplicate, D. floridana as dorsally uniplicate. 
Now dorsal biplication is brought about by the dorsal sulcus being 
superimposed upon a single dorsal fold. In D. septigera, as well as in 
D. floridana, a broad ventral sulcus is superimposed upon a dominant 
ventral fold ; these two species, therefore, are, in my opinion, ventrally 
biplicate (as in Magellania flavescens and some others). 
This confusion of folding has led Thomson to question the generic 
position of Zerebratula grayt, Dav., which was also referred to Dallina 
by Beecher.? This is a ventrally uniplicate species with alternate 
multicostation, and according to Thomson cannot belong to Dallina. 
He further states that ‘‘ there seems to be no difficulty in referring it 
to Magellania, as it apparently possesses the Magellaniform hinge- 
plate and cardinal process”. ‘There is some mistake here; the 
hinge-plate is not Magellaniform. Davidson’s figure ? is misleading. 
There is no hinge-plate such as occurs in the genotype of Magellania 
(I. flavescens). A mesial septum is present, extending from about 
the middle of the dorsal valve to near the apex, where it merges with 
slight bifurcation into a thick deposit, on the floor of the valve. 
_ From each side of this deposit the dental sockets and crural bases 
arise ; the cardinal process is transverse and weak. Apart from this 
* “Brachiopod Morphology: Types of Folding in the Terebratulacea,’’ 
GEOL. Mac., Dec.- VI, Vol. II, February, 1915,-pp. 71-6; ‘‘ The Genera of 
Recent and Tertiary Rhynchonellids, ” ibid., September, 1915, pp. 387-92. 
2 “* Revision of the Families of the Loop- “bearing Brachiopoda » and ‘‘ The 
Development of Terebratalia obsoleta, Dall’?: Trans. Conn. Acad. Arts and 
Sei. -, 1x, pp. 376-99, pls. i, ii, 1893. 
aes Monograph of Recent Brachiopoda’’: Trans. Linn. Soc. London ; 
ae (2), iv, pl. x, fig. 3, 1886-8. 
