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have been washed in from other levels of depth, their usual 

 habitats. The Plicatulce are so frequent that they recall to mind 

 the marnes aplicatules Marcoii, at Cernans (Salins) in the Jura. 

 Many varieties, too, of this very changeable genus may be 

 observed, since numerous examples turn up which prove that 

 the future career of the shell is determined by accident. If the 

 spat of the Plicatula happen to adhere to a smooth foreign body 

 like a Belemnite or Terehratula, forthwith it grows up to be free 

 from spines or tubercles. Thus moulded by circumstances P. 

 spinosa becomes the smooth Plicatula sarcinula, &c., &c., with 

 little or no ornamentation. Under our name, the Plicatula 

 spinosa, it is held* that there are two species : our Middle Lias 

 species is the Plicatula {Harpax) Parhinsoni, and the Lower 

 Lias species is called the Harpax spinosus. In the former the 

 spines are on one side the attached valve ; in the other, the 

 H. spinosus, the spines are on both valves, and the shell is larger. 

 I must frankly own that my limited experience does not support 

 this view ; for, as to size, our Lower Lias species is smaller than 

 the Middle Lias examples, the Spinatus Zone specimens are 

 double the size and, in other respects, the distinction seems to 

 fade before the examination of a large suite of examples. Still 

 the names are given here to incite to further observation. A 

 beautiful little Pecten is yielded by the sands ; the P. pumilus — 

 Lamakck ; the P. amalthei, of Dumoetier, Oppel, and Stoliczka. 

 Brauns says it is an Inf. Oolite species, and is very rare in the 

 Middle Lias : it is certainly rare here. Its peculiarities would 

 require a lengthy disquisition. The large species of the Pleur- 

 onectes division, Pecten lunularis, which attains such a fine size in 

 the Margaritatus Zone, is rare and small ; but there are several 

 species of ribbed Pectens, such as are determined and given in the 

 general list of the fauna, as well as Cypricardia, Cucullcea, 

 Isocardia, Unicardium, Inoceramus, &c., &c. 



(d) Brachiopoda — For this order of Mollusca, sands or sandy 

 marls, unless firmly resting upon a very tranquil sea-bottom, 

 do not favour their chance of propagation ; they can have no 



* J. A. Eudes Deslongchamps, Essai sur les Plicatules fossiles des terrains du 

 Calvados, &:c. Caen, 1858. 



