MOLLUSCA (except CEPHALOPODA). 135 



Pterocera oceani, Plearotomaria riigata, Sowerhya Diikei, Gallery 

 Astarte ntgosa, and many species of Trigonict. Note also VIII. 

 the laroje borins^s of Litliodomus. 



The shells of the Kimmeridge Clay are mainly from Table-case 

 Weymouth, Dorset ; Wootton Bassett, Wilts ; the neighbour- 10- 

 hood of Oxford ; and Hartwell, Bucks. The following are 

 noteworthy : the large Pleurotomaria reticulata, the D-shaped 

 Ostrea deltoidea, the common and characteristic Exogyra vir- 

 gula, Gryphaea dilatata with its thickened hinge, well shown 

 in sections, a Gryphaea with a supposed pearl, Protocardia 

 [Cardium\ striatida, Astarte hartwellensis, various Trigonias, 

 Goniomya literata, and Thracia depressa. A slab of Kim- 

 meridge Clay filled with Ostrea laeviuscida is on the wall, Between 

 and below it is the fine block of Coralline Oolite with over Wall-cases 

 110 shells of Trigonia clavellata figured in Damon's " Geology 6 & 7. 

 of Weymouth" (see our Plate VI.). 



The Coral Kag and Calcareous Grit are the chief British 

 rocks formed during Sequanian or Corallian time; they 

 stretch across England, with occasional breaks, from Wey- 

 mouth to Buckinghamshire, reappearing in Yorkshire, and 

 are rich in fossils. Among the gastropods are Bourguetia Table-case 

 [P]iasianella\ striata, Pseudomelania heddingtonensis, Nerinaea 10. 

 Goodhalli, and a spiny winkle Littorina muriccUa. Lamelli- 

 branchs are represented by Alectryonia gr eg aria, Chlamys 

 vimineus, Ctenostreon pectiniformis, Mytilus 'pectinatus, Tri- 

 gonia triquetra, and many others. The numerous borings of 

 Gastrochaena and Litliodomus in the coral masses bear witness 

 to a shallow sea. It is interesting to contrast the richness 

 and variety of the molluscan fauna that lived in the Corallian 

 sea with the comparatively few species found in the clays 

 above and below. 



The clay below is the Oxford Clay, well developed in 

 Oxfordshire, and forming a more continuous band across 

 England from Dorset to Yorkshire than do the Corallian 

 limestones. Within this tract the fossils are entirely marine, 

 and those exhibited come chiefly from Weymouth, Christian Table-case 

 Malford and Chippenham in Wiltshire, and Scarborough. 11. 

 The delicate character and shelly constitution of the Wiltshire 

 specimens contrast with the coarser and stony appearance of 

 the others. Characteristic forms are Alaria trifida with its 

 long processes, the delicately spined Spinigera spinosa, Nucida 

 ornata, Volsella \Modiola'\ cuneata, and Pleuromya recurva. 

 Under Ostrea and Gryphaea are to be seen shells that have 

 grown upon Trigonias and an ammonite and have assumed 



