Vol. 56.] AXD OLDHAMIA. 2813 



Oldhamia is usually represented in sections by simple grooves, cases 

 occasionally are found in which the sides of the groove are raised 

 into overfolded lips, which sometimes meet and enclose an elliptical 

 space. 



A singular structure, which I at first explained as indicating the 

 presence of the excreta of worms, may next be described (PL XIX, 

 figs. 14 & 16). In the midst of the thin parallel laminae of the rock, 

 certain markings arrest the attention by their definite circular out- 

 line ; they vary considerably in size, but most of them are between 

 0*2 to 0*5 mm. in diameter ; on closer examination many are found 

 with an elliptical outline, and some bounded by an irregular closed 

 curve. Not infrequently a concentric arrangement of lighter and 

 darker particles may be observed within the outer boundary, and 

 occasionally radiating lines which proceed from the centre outwards. 

 A large circle often includes a number of smaller circles within it, 

 and adjacent circles may intersect each other. These appearances 

 are due to a definite arrangement of the minute particles which con- 

 stitute the rock. Sometimes the markings are dark on a light ground : 

 in such cases short lines and dots of ferric hydrate, and minute 

 granules of opaque yellowish-white material (possibly decomposed 

 felspar, possibly leucoxene), most obviously determine the outline. 

 In other cases the markings are light on a dark ground : these are 

 due to a circular arrangement of minute scales of mica and chlorite ; 

 in one or two instances a radiate arrangement of sericite-scales has 

 been observed. On first examination these remarkable forms seem 

 to be scattered haphazard through the rock, but in good specimens 

 careful observation shows that they tend to run in lines, sometimes 

 parallel to the lamination, but more often across it. Sometimes a 

 concentric system of circles fills an Oldhamia-grooYe, sometimes 

 such a system lies immediately below, but connected with the groove 

 by a narrow neck ; or again several rows of circles branch out root- 

 like from the floor of a groove, and not unusually such rows are 

 bounded on each side by fine parallel opaque lines, when the struc- 

 ture recalls the appearance of a racemose gland. These systems of 

 curves traverse the laminae without disturbing their course, and are 

 as circular in transverse as in horizontal sections. Further, although 

 best displayed in the Oldliamia-be&s they are to be met with in a 

 great variety of fine-grained rocks. Some difficulty may be ex- 

 perienced in first recognizing them, which may account for their 

 having hitherto escaped notice, but once pointed out they become 

 sufficiently obvious. They may be seen both by transmitted and 

 reflected light, and are easily photographed. 



It is not unnatural to regard the 'balled' structure suggested 

 by these markings as indicating the excreta of worms, particularly 

 as we are assured that the majority of deep-sea animals live by 

 eating the mud at the bottom, and that every particle of mud of 

 the sea-floor has at some time passed through the intestine of a 

 worm. While recognizing that a possible explanation may lie in 

 this direction, I am more disposed to regard the balled structure 



