202 Dr. Alex. Brown — On Solenopora. 



specimen, however, was so mucli destroyed, that one could not, 

 with certainty, decide as to the true state of matters. Further 

 examination of such specimens will clear up all doubt as to the 

 existence of these spaces. In the same sections are seen clusters 

 of cells at intervals, arranged in rosette-like fashion (Fig. 6). One 

 is impressed with the striking similarity all this bears to the con- 

 ceptacle-spaces and the canals of Lithothamnion (Figs. 8 and 9), the 

 rosette-cells of Solenopora representing the similarly arranged cells 

 around those canals. It is, therefore, highly probable that the spaces 

 observed in S. Jurassica are really the remains of once existing con- 

 ceptacles, and that the rosette-cells surrounded the passages leading 

 into them. It will, however, require further and more extended 

 observation to confirm such conditions as these. 



(d.) Modes of Occurrence. 



It may be objected that these forms, here referred to the genus 

 Solenopora, are not in fact generically identical. Such an objection, 

 however, must fall to the ground, for it is impossible to overlook 

 the fundamental likeness which subsists among them all. They 

 are found under the same conditions, associated in the same kind 

 of rocks, and taking part in the formation of the same great masses 

 of limestone, whether they belong to the Ordovician, the Silurian, 

 or the Jurassic systems. They have, too, the same external charac- 

 teristics, having the appearance of pebbles or concretions, with a 

 lobulated or subspherical outline. On fracture the surfaces of all 

 present a porcellanous or fibrous aspect, and exhibit the charac- 

 teristic concentric structure. Many of the Solenopora limestones 

 show scarcely any differences in outward and internal appearance 

 from the ordinary Nullipore limestones ; and, indeed, it is often 

 very difficult to distinguish between them. 



(e.) Difficulties in retaining the genus Solenopora in the Animal 



Kingdom. 



In assigning the genus Solenopora to a definite place in the scale 

 of life, it seems clear that, if an animal at all, it must be referred to 

 some group or other of the Coelenterates. But no recent Ccelenterate 

 has zooidal tubes as minute, or nearly as minute, as are those of 

 Solenopora. This is the great difficulty in assigning to the genus 

 a place in the Animal Kingdom. Still more, were it of animal 

 origin, would it be difficult to account for the largely branched 

 cells of Solenopora dendriformis, the fusiform cells of Solenopora 

 fusiformis, and the essentially cellular nature of the skeleton in 

 well-preserved examples. Taking all the evidence as we now have 

 it, we may reasonably conclude that the genus cannot be referred 

 to the Actinozoa ; and " we cannot refer it to the Hydrozoa, for 

 we are not acquainted with any Hydrozoon, living or extinct, with 

 which Solenopora could be compared. It shows no features in its 

 minute structure which remind us of the Hydrocorallines, and it 

 assuredly presents no structural resemblance to any known type 

 of the Stromatoporoids " (Nicholson). 



