A. R. Horn-ood — Archarenicola Bhcetica. 397 



the impression. There is, in fact, no sign of crotchets opposite the straight 

 cheetse. These last are short, barely 5-6 mm. long, and are borne in fascicles 

 so closely associated that they cannot be counted. They are not visible in 

 every part, but are indicated by folds in the matrix, which may be taken to 

 show their position. Within the broken portion of the body-surface in the 

 posterior part are some detached chsetse of a similar nature. As a rule they 

 bear a strong resemblance to the chsetse of Arenicola marina. It is not possible 

 to distinguish any spathulate chaetse similar to those in Arenicola. As a whole 

 they bear a resemblance to the parapodia of Nereis, but are not present on each 

 annulus as in Nereis, and the annuli themselves do not show any trilobed 

 divisions as in that genus. The appendages in fact most nearly approach those 

 of Arenicola. 



Surface. The surface of this fossil for 4'5 cm. of its length is the original 

 cuticle of thick cells which now preserve only the form and arrangement of the 

 external somites and annuli and the epidermal surface characteristics. The 

 upper portion, l'5cm., is a cast of the inner surface of the cuticle, and 

 possesses no surface features. As the anterior epidermis of this specimen is 

 wanting, it is impossible to say whether it was like the lower part or not. 



In Arenicola the anterior and middle part of the cuticle is divided up into 

 well-marked contiguous polygonal areas which give it a wrinkled appearance. 

 In the tail the cuticle is covered with prominent papillfe similar to the anterior 

 arrangements in structure, and doubtless derived from similar definite polygons, 

 originally, becoming rounded or sharply defined with age. 



In the specimen A the cuticle is covered with raised papillge which do not 

 occur on the matrix itself, and are impressions of the papillae found in A?-enicola 

 on the tail part. Whether this type had papillss alone or on the anterior part 

 remains to be investigated. But this worm must have presented in this and 

 other characters already noted a very strong resemblance to the modern lug- 

 worm. The anterior third representing the inner surface retains traces in 

 part of the inner tissue, belonging perhaps to the longitudinal muscles, but 

 there is no structure preserved, as everything, except perhaps some chitinous 

 chsetse, is replaced by the black shale matrix. 



An exception may be made to the last statement perhaps in the case of the 

 brown layer or ring surrounding the impression itself posteriorly. It is almost 

 certain that this has been produced by a similar substance to the green or 

 yellow pigment which is exuded in recent lugworms by the skin. It is thought 

 by Ashworth to be a lipochrome. Another brown or black pigment insoluble 

 in alcohol is like melanin in this respect, and may be derived from the yellow 

 lipochrome. Indeed, FarroU showed that melanin could be due to chemical 

 change in lipochrome under the influence of an acid. The further homology 

 thus afforded by the probable identity between the brown stain and the pigment 

 exuded by Arenicola makes the resemblance irresistible. 



Head portion. In endeavouring to uncover part of the impression I f oftnd 

 on the left side, in the posterior portion, an impression and counterpart of 

 a terminal part of a similar annelid. This exhibits all the characters of the 

 figured portion, and may be taken to be the head or anterior portion. No 

 details as to the proboscis, peristomium, or other parts can be made out, as it is 

 badly preserved, but there is a cast of what may be regarded as a protruding 

 prostomium with a bifid apex, the lines of the straight stem or base of the 

 prostomium being deeply impressed as two parallel lines, whilst the apex is in 

 bas-relief ; and as the other portion in alto-relievo does not show this, it is not 

 possible to be absolutely certain as to the real outline of the structure. It is not 

 exactly like that of Arenicola, but bears a considerable resemblance to it. The 

 buccal papillee of the proboscis, which is not clearly present, are not to be seen, 

 so that it was not protruded. Had this worm been a Nereis, which the head 

 portion might have indicated, it would have exhibited palps and tentacles and 

 peristomial cirri, which Arenicola does not possess, and as there is no sign of 

 these the homology in this instance again may be taken to be correct. It is 

 fortunate indeed that this terminal portion came to hand, since it settles a point 

 as to which otherwise there might have been difference of opinion. 



