74 THE HABITAT OF THE EURYPTERIDA 



their distribution, origin and their included organic remains. In re- 

 gard to the origin he says: "The rivers which discharge into the 

 Severn estuary, draining, as they do, a catchment basin of 9193 square 

 miles, are the chief sources of supply" (264, 611). A source of sec- 

 ondary, but by no means slight importance is the sea, which has worn 

 off material from the cliffs and which has carried muds into the Sev- 

 ern. As Sollas has fully explained, though the details canno here 

 be given, a small part of the silt which is brought down by the rivers 

 may be deposited in the estuaries themselves, but the greater por- 

 tion is carried seaward, "so that the final resting-place of the sedi- 

 ment of the Severn is situated some distance out to sea." A micro- 

 scopic examination of the muds from a large number of localities on 

 both sides of the Severn and along its tributaries revealed the follow- 

 ing organic remains: "Coccoliths and rarely coccospheres, both of 

 the ordinary cyatholith type so common in adjacent seas and in the 

 Atlantic ooze; Foraminifera such as Miliola, Textularia, Nonionina 

 crassula, Polystomella umbilicata, Rotalia sp., Spirillina sp. . . . 

 spicules of Alcyonaria rarely; fragments of Echinoderm skeletons and 

 minute spines: and triradiate spicules of Calcisponges, probably de- 

 rived from Sycandra ciliata and S. compressa. The siliceous constit- 

 uents are chiefly sponge-spicules, very rarely Radiolaria, and a 

 variable quantity of Diatoms." The remarkable feature about these 

 remains is that they are all marine, and yet they sometimes occur on 

 the banks of the rivers at a great distance from truly marine waters. 

 Moreover, the remains which are found are of organisms not living 

 within many miles of the places where they occur, for Sollas has car- 

 ried out a careful investigation of the fauna along the coast. He 

 says: "Sponges do not grow anywhere so near Bristol on this side 

 of the Channel as Portishead and Weston; Lynton, which is about 

 60 miles away, is the nearest possible locality; while Ilfracombe, 

 about 15 miles further west, is well known as a rich collecting ground 

 for both siliceous and calcareous sponges, and a host of other marine 

 forms, including sea urchins and starfish, which might well furnish 

 the echinoderm network and spines so frequent in the ooze. On the 

 other side of the channel one would need to go to Bridgend before 

 meeting with much in the way of shore life, and I doubt, after a hasty 

 visit to that locality, whether much would be found there; a good deal 

 farther west is Tenby, and no naturalist needs to be informed of the 

 luxuriant growth of all kinds of marine animals, including sponges 

 to be met with there" (264, 619). Sollas clearly shows that the 



