396 A. M. Honcood — Arcliareiiicoia Rhcetica. 



As to the first group the burrows, such as Bilohites, Husichnites, 

 Arthrichnites, Protichnites, Climacticfniites, Scolithus, have been 

 regarded also by Dawson ' as due to the movements of various 

 Invertebrates and not as Annelid burrows especially. Sahelhrites he 

 described as a new sand-tube, and Butkrotrephis as a true Fucoid from 

 the Siluiian. 



The similarity between such impressions and those of the markings 

 made by Molluscs and Crustacea had been pointed out by Professor 

 McKeuny Hughes,- so that a great clearance has been made of some 

 of the old lumber that cumbered the ground in the domain of fossil 

 Annelids. 



Though this Annelid with its cuticular investment constitutes a new 

 group, I think it unnecessary to make a third for its reception, 



Notes on Specimen A. (PI. XXT, Fig. 2.) 



Size. Extreme length, 6 cm. Greatest width (upper end), 18 mm.; at 

 centre, 16 mm. 



Measurements bettveen annuli. Distance between annuli, 1-2 mm. (5 to a 

 centimetre) . 



The distance between the annuU varies irregularly ; there are some shorter 

 furrows between longer ones, especially in the anterior half, which is the under- 

 side of the raised or relief portion. 



In shape it is a vermiform impression, slightly curved from below to the left. 

 The impression being flattened, it is difficult to estimate the real diameter or 

 girth of the animal originally. Compressed it forms a thick impression 3 mm. 



The posterior portion has a stained outline, 5 mm. thick, on the right side, 

 due to the exudation of animal matter or juices from the soft body preserved in 

 the mud in some combination which is probably bituminous. A portion of the 

 left posterior margin also shows the same character. Wherever the impression 

 is preserved in the Black Shale the same greenish-brown external outline may 

 be seen. 



Segmentation. The term annuli has already been given to the transverse 

 ridges that regularly cross the body. Whether it is possible to distinguish the 

 definite arrangement of these annuli into segments, each consisting of so many 

 annuli, cannot be determined owing to the manner of preservation. In 

 Arenicola, of which I regard this fossil as a prototype, there are five annuli in 

 each segment, one being larger than the rest and bearing the parapodia. As 

 already noticed there is in specimen A a certain differentiation into two sizes, 

 a large and a small annulus alternating. And to all appearance the appendages, 

 ehfetigerous parapodia, are attached to the base of the larger annulus. But on 

 this point it is impossible to speak with absolute certainty. In Arenicola there 

 are three segments in front of the one bearing parapodia and one behind, 

 and it is possible that the intercalation of three acliEetous segments is a new 

 feature gained during the evolutionary progress of the genus, or that the 

 apparent arrangement of alternate large and small segments is a variation of it. 



Appendages. The body of Arenicola may be divided into three regions^ — an 

 anterior with parapodia, without gills, a middle portion bearing both, and a 

 posterior achaetous portion. 



The portion of the body to which specimen A may be said to correspond is 

 the anterior non-branchiate portion. Though at first it appeared to be achsetous, 

 this portion does undoubtedly exhibit appendages which correspond to the noto- 

 podial setae of Arenicola. If the capillary appendages on either side seen at 

 intervals are notopodial setse, the neuropodia must be invisible and beneath 



' "On Burrows and Tracks of Invertebrate Animals in Palaeozoic Eocks and 

 other Markings " : Q.J.G.S., 1890, p. 595. 



^ "On some Tracks of Terrestrial and Freshwater Animals": Q.J.G.S., 

 1884, p. 178. 



