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



Nereidina, MacLeay. 



These are the most perfect in their structure of all Annelida, 

 as they possess numerous organs and have a distinct head, 

 which is generally provided with eyes and antennae. Some of 

 them, after the manner of Serpulina, inhabit tubes, which 

 tubes are membranaceous, and formed by a transudation from 

 their body ; but in general the Nereidina are naked, and they 

 are always agile animals freely moving about in search of their 

 prey. Aristotle calls them, ^' ^KoXoTrevSpav OaXdo-acac ira- 

 pa'K\r](jiai rS etSec rah ')(epaa[aL^,'^ (Lib. ii. c. 121.) ; and it 

 is true that they are wonderfully like Centipedes. The fossil 

 impressions in the Llampeter Rocks, are too indistinct to 

 enable us to determine very accurately the genera and species 

 of Nereidina which there occur, more particularly as the ge- 

 neric characters in this group depend on such minute distinc- 

 tions as are afforded by a study of the mouth, antennae and 

 eyes. I shall therefore consider the impressions fig. 1. and 

 fig. 2. Murchison, Sil. Sys. to belong to the 



Genus NEREITES. A genus which comes very near to 

 Savigny^s genus Lycoris in its external appearance, 

 only the segments of the body are here perhaps more 

 slender and in proportion longer than usual. 

 Spec. 1. Nereites Cambrensis. Murch. /i. s. 



The body of this species seems to have consisted of about 

 120 segments. The feet were half the length of a seg- 

 ment of the body, and the cirri of the feet were longer 

 than such segment. — ib, PI. 27- f. 1. 

 Spec. 2. Nereites Sedgwickii. Murch. n. s. 



Body much more slender than that of N. Cambrensis, and 

 apparently consisting of a greater number of segments. 

 These segments have the feet attached to them appa- 

 rently inconspicuous, although the cirri are very di- 

 stinct. PI. 27. f. 2. 

 N.B. The impression now under consideration was clearly 



some Annelida are not provided with red blood ; but the distinguished Sa- 

 vigny stated the same fact so long ago as the year 1 823, for in his Systeme 

 des Annelides he places Clepsme among his Hirudinees. Nay, even Cuvier, 

 who first distinctly pointed out the group under the name of vers a sang 

 rougey has said that their blood is only generally red. Although herma- 

 phrodites, many of them require a reciprocal coitus. 



