50 POST-TERTIARY ENTOMOSTRACA. 



The gravel has chiefly been derived from the sandstones of the neighbourhood, with 

 fragments of quartz and mica-schist, and the greater portion is less or more water-worn 

 and striated. 



In our list of Mollusca sixty-one species and seven varieties have been identified. 

 The two prevailing shells are Feden Islandicus and Mytilus modiolus, but perhaps the 

 shell of most geological interest in this deposit is Pecten maximus, as it has been 

 considered doubtful Avhether it lived at the same time in the Clyde beds with Pecten 

 Islandicus or at a subsequent period. Questions have been raised regarding P. maximus, 

 which show the necessity of extreme care in cataloguing supposed '' glacial " fossils of 

 any description. 



It is very doubtful, indeed, whether P. maximus belongs to the group of shells 

 found in the true glacial clays. 



1. It is not uncommon as a hving species in the Frith of Clyde, and its valves abound 

 in the upper silts and raised beaches, and specimens really belonging to the younger beds 

 may have been accidentally mingled with the older fossiliferous deposits beneath. From 

 such mixtures catalogues of species from the " Clyde beds " have often been augmented. 



2. There is a Pecten maximus bed (presently to be described) immediately in contact 

 in some localities with the older Arctic shell-clays on which it rests. 



3. Balani have never been found attached to P. maximus, yet in the glacial beds 

 they are common on P. Islandicus ; and as B. porcatus and B. crenatus (which are 

 remarkably large and abundant in the Arctic clays) do not seem at all fastidious in 

 their choice of attachment, whether to a stone or shell, we may reasonably infer that 

 most of the shells of P. maximus found in the Clyde beds were not cohabitants with 

 P. Islandicus. 



4. With the exception of the one valve met with at Carts dyke, P. maximus has 

 only been found in beds between high and low water which have been greatly disturbed 

 and re-arranged again and again by storm and tide. 



This argument regarding P. maximus has been given to show the necessity of great 

 caution in making deductions regarding the percentage and range of species generally in 

 the whole series of glacial beds. Whether such deductions are made from the Ostracoda 

 or the Mollusca, the same argument applies with equal force. 



Height above the sea ten to twelve feet. 



The following Ostracoda were found 



Argillcecia cylindrica, G. 0. Sars. 

 Pontocypris mytiloides (Norman). 

 — triyotiella, G. 0. Sars. 



