Mr. W. S. MacLeay on the Annelida. 387 



that of an animal, as wiU appear by the figure, where the worm 

 has evidently, before coiling, with difficulty trailed itself along 

 in the mud, in a way, which any one accustomed to collect 

 these Annelida will at once recognise. 



Genus MYRIANITES. 



Body linear, very narrow, and formed of very numerous 

 segments with indistinct feet and short cirri. 



Spec. 1. Myrianites MacLeaii. Murch. n. s. — PL 27. f. 3. 



N.B. The softness of the texture of the foregoing three 

 species of Annelida and the perfection of the impression in 

 fig. 1 . make it very remarkable, that if articulated feet existed 

 in the Trilobites, some vestiges of them, even although mem- 

 branaceous, should not have come down to us more perfect 

 than those figured by Goldfuss. (See Ann. Scienc. Nat. vol. xv. 

 PL 2. f. 8. and pp. 665, 66? ante.) 



Serpulina, MacLeay. 



These are sedentary animals without eyes or antennae. They 

 live in tubes which are either a natural transudation of their 

 body, and are either membranaceous or calcareous, or their 

 tubes are semifactitious, being then composed of an aggluti- 

 nation of particles of sand or other small substances. The cal- 

 careous nature of the tube in some Serpulina is very advan- 

 tageous for their preservation, and has thus enabled us to see 

 that such animals occurred frequently in the Upper Silurian 

 Rocks. 



Genus SERPULITES. 



Spec. 1. Serpulites longissimus. Murch. n. s. PL 5. f. 1. 

 Very long, hardly diminishing in diameter, compressed, 

 smooth, slightly tortuous, composed of numerous thin 

 layers of shell containing much animal matter. 



No part of this extraordinary fossil has been observed at- 

 tached to other bodies ; it forms large curves, sometimes al- 

 most circles, occasionally even a foot in diameter. The tube 

 is so much compressed that its sides nearly touch, and that this 

 is the effect of pressure is shown by the form it has assumed. 

 Those parts which were nearly perpendicular to the direction 

 of the compressing force have resisted pressure most power- 

 fully, and fractures have taken place in longitudinal lines near 



