ON CERTAIN VERMIFORM FOSSILS, 23 



consequently, the surface has generally an imperfect or worn 

 character. The extremities are not often seen ; they are abruptly 

 and irregularly rounded. This is the form more particularly de- 

 scribed by Mr. Wood, who has in his possession the fine speci- 

 men figured in PL V., which measures nearly eight feet in length, 

 though neither extremity is perfect. 



The fourth form (PL VII. «), which seems to be the dominant 

 one in Northumberland, and is that figured and described by 

 Mr. John Dixon, is, as far as I have been able to ascertain, 

 usually in relief upon the upper surface of the lower slab, from 

 which it never deviates; it is considerably depressed, and is 

 grooved (&), or ridged (PL VIII. fig. 1 , a) along the middle line, 

 and is occasionally very long. The specimen figured in PL VII. 

 measures upwards of six feet in length, but was probably much 

 longer, for the extremities are not present. In fact, it has not 

 yet been determined to what length these fossils extend, as none 

 hitherto measured have had both ends 'perfect. Large speci- 

 mens are frequently an inch wide, and generally much undu- 

 lated, and occasionally, but never intricately, convoluted. 

 Such have the surface most frequently marked with 

 numerous, regular, rather fine, transverse stri^, or arched 

 ridges (PL VIII. fig. 2), which are sometimes very delicate and 

 close set, though they vary in these particulars, and are occa- 

 sionally coarse and irregular, giving to the whole surface a 

 wrinkled appearance. Small specimens (fig. 1) on the contrary 

 are frequently wound up in an intricate manner, the folds being 

 well rounded and often convoluted; but the surface is never 

 marked with transverse lines or wrinkles. 



It is this last form, particularly the smaller and more com- 

 plicated variety, that so closely resembles the track of Sulcator 

 arenarim (PL III. fig. 1). The folds or windings are precisely 

 similar, and so is the median groove. It differs chiefly in being 

 occasionally much larger, and in rising up more boldly in relief 

 from the matrix, though in these respects they sometimes closely 

 approximate. Dimensions, however, can be of very little con- 

 sequence, for of course, the larger the animal the larger the 



