158 PALEONTOLOGY 



writer has interpreted to be those of a large entomostracous 

 Crustacean ;* in evidence of which the following sample, appli- 

 cable to a single species, may be given, in illustration of the 

 ichnologist's mode of work. 



Protichnites. 



Protichnites septem-^notatus (fig. 64). 



The subject so named consists of a series of well-defined 

 impressions, continued in regular succession along an extent 

 of 4 feet ; and traceable with an inferior degree of definition, 

 along a further extent of upwards of 2 feet. 



In the extent of 4 feet there are thirty successive groups 

 of footprints on each side of a median furrow, which is alter- 

 nately deep and shallow along pretty regular spaces of about 

 2i inches in extent. The number of prints is not the same in 

 each group ; where they are best marked, as in fig. 64, 1 L, 

 we see 3 prints in one group, a, a, a", 2 prints in the next, b, 

 b\ and 2 in the third, c, c, which is followed by a repetition of 

 the group of 3 prints, a, a, a", making the numbers in the 

 three successive groups 3, 2, 2 ; the three groups of impres- 

 sions being recognizably repeated in succession along the 

 whole series of tracks on both sides of the median groove. 



The principal footprints are disposed in pairs, placed with 

 different degrees of obliquity, in each of the three groups 

 towards the median track ; the innermost print in the second, 

 B, and third, C, pairs, which are best marked, being usually 

 rather more than half the size of the outer print, V and c. 



The two footprints of the same pair are a little further 

 apart from each other, in the three succeeding pairs, as at «', 

 a", b, b', c, c, especially in the second and third groups of each 

 set ; the two forming the pair a', a", again approximating in 

 the next series, and the pairs b, b' and c, c, diverging in the 

 same direction and degree ; and this alternate approximation 



* Quarterly Journal of tin- Geological Society, vol. viii., p. '214, 1852. 



