LR. Etheridge, jun.— Carboniferous Tubicolar Annelida. 219 
‘many are found in salt water.” The bearing of these remarks on 
the question of the habitat of our Spirorbis, one of the most 
characteristic fossils of the Coal-measures, I consider to be of the 
greatest importance. 
The observations of Dr. Dawson on the accumulation of the South 
Joggings Coal-measures, although given from a different point of 
view, are equally important. Considering them to have been 
deposited in swamps and lagoons, he says,’ the events indicated by 
the 8. Joggings section “consist of a long succession of oscillations 
between terrestrial and aquatic circumstances, and unaccompanied 
by any material permanent change in the nature of the surface, or 
in its organized inhabitants. .... The results of these opposing 
forces no doubt always existed contemporaneously, so that by a mere 
change of place, one could have passed from a coal swamp to a 
Modiola-lagoon, or a tidal sand-flat; but in each separate locality 
they alternated with each other, with greater or less frequency, etc.” 
Such alternations of an aquatic nature from salt to fresh or brackish 
water conditions would have been peculiarly fitted, I believe, for 
the development of such a form as Micro. carbonarius. My father 
has pointed out the co-occurrence of a purely marine Crustacean of 
the Limuloid type, Prestwichia rotundata, with Ificro. carbonarius, 
in the Somersetshire Coal-field,*? the latter being parasitic on the 
carapace of the former. 
Finally, it is almost needless to observe, the Annelida are both 
marine and fresh water, and even amphibious, as, for instance, the 
Hairworm (Gordius). It is not impossible, therefore, that Jicro- 
conchus, although of a different order, may have been so also. 
Microconchus pusillus varies considerably within certain limits. 
The typical form is well illustrated by the four upper left-hand 
figures of Murchison’s Siluria.* The variety with the last turn of 
the coil prolonged is equally represented by his two lower figures. 
Variation also takes place in the mode of attachment to foreign 
bodies—whether by only a portion of one side of the coil, seen as a 
groove in one of Murchison’s figures, or by the whole of one side of 
the tube, which then becomes flattened. The surface ornamentation 
is equally subject to variation; it is at times almost plain, at others, 
with very numerous, fine, but regular and distinct direct transverse 
strie, almost resembling microscopic ridges; whilst again in some 
specimens fine spiral striz occur; this condition has been well 
figured by Murchison. 1 have not observed the beaded. form of 
ornament described by Dr. Dawson as seen in Canadian specimens ; 
this may, however, arise from the intersection of the fine transverse 
ridges and spiral strive. 
The tube of this species is dextrally coiled, but in many figures 
individuals will be seen scattered over the surface of a plant appa- 
rently sinistral. This appearance has been explained by Dr. Dawson, 
who, speaking of his S. Hrianus, says that the tube will appear 
1 Quart. Journ. Geol. Soc. x. p. 29. 
2 Trans. Manchester Geol. Soc. 1866-67, vi. p. 124. 
3 “ Siluria,” 4th edition, 1867, p. 302, Fossils (83). 
