THE JURASSIC DEPOSITS WHICH UNDERLIE LONDON. 761 
Cylindrites, and other univalve shells. In the Richmond clays 
Gasteropoda are very rare, but a few are found in the limestones. 
Fragments of full-grown Lamellibranchiate shells abound in the 
Richmond washings. Except, however, in cases like that of Pecten 
rushdenensis, Lyc. & Mor., where the surface-markings are of a very 
distinct and characteristic pattern, it is very difficult to determine 
the species to which they belong. The young forms which occur 
both at Richmond and at Meux’s Brewery usually afford very 
unsatisfactory evidence concerning the species to which they should 
be assigned. 
With the Brachiopoda, however, the case is different. Mr. T. 
Davidson, F.R.S., has kindly examined the specimens and supplied 
me with notes from which he has permitted me to quote. 
The most characteristic shell in the Richmond deposits was the 
Terebratula coarctata, Park. A very perfect specimen, measuring 
123 millim. broad by 12 millim. high, was found with many 
fragments of adult shells, and young specimens in every stage of 
growth. The large and perfect specimen is described by Mr. Davidson 
as being “a very typical example of the species.” The spines on 
its surface are exquisitely preserved. I have not found 7’. coarctata 
among the washings from Meux’s well. 
Terebratula maxillata, Sow., is also very abundant in the Great 
Oolite of Richmond. An adult shell of this species occurs in one of 
the beds of limestone beneath Richmond at a depth of 1219 ft.; it 
measures 48 millim. in breadth, and 45 millim. in height, but is 
slightly crushed. Fragments of this shell, often overgrown with 
Bryozoa, occur in the clays, with prodigious numbers of the young 
form of the shell. Of these young forms Mr. Davidson writes, 
«JT have carefully compared these small specimens, and believe them 
to be the young forms of Terebratula maxillata, a form that occurs 
along with 7. coarctata. At Hampton Cliff near Bath, in the Great 
Oolite, similar young forms may be collected by hundreds.” Lhwyd, 
as Mr. Davidson points out, has figured a series of specimens from 
Hampton Cliff in his ‘ Lithophylacii Britannici Ichnographia,’ pl. ix., 
showing the transitions from the young to the adult forms. Mr. 
Davidson failed to find among the Richmond specimens any that 
were referable to Terebratula Buckmani, aform which at Hampton 
Cliff occurs with 7’. maxillata. The young forms of 7. maaillata 
occur in the washings from Meux’s well, but are much rarer than 
at Richmond. 
Terebratula digona? Sow. Among the small Terebratule from the 
Meux’s-well washings are several which appear to be the young 
of 7. digona. 
Rhynchonella concinna, Sow., sp., isrepresented at Richmond by a 
few fragments of the adult shell and anumber of young ones. Both 
were identified without hesitation by Mr. Davidson. The young 
forms occur in the washings from Meux’s well. 
The interesting forms of Thecidium and Zellania found by Mr. C. 
Moore in the material from Meux’s well did not occur in that 
from Richmond. 
