The specific name _mamillosum_ has also been given to a recent species by Hauck[359], but probably in ignorance of the existence of Gümbel’s Cretaceous species. • • • • • 2. _Lithothamnion suganum_ Roth. Fig. 37, B. The section of this form given in fig. 37, B shows three oval conceptacles filled with crystalline material. The two lower conceptacles originally communicated with the surface of the thallus, but as in recent species the deeper portions of the algal body became covered over by additions to the surface, forming merely dead foundations for new and overlying living tissues. The cells of the thallus have a breadth of 7–9µ, and a length of 9–12µ. The specimen was obtained from a Lithothamnion bank, probably of Upper Oligocene age, in Val Sugana[360], in the Austrian Tyrol. Numerous other species of Jurassic, Cretaceous and Tertiary age might be quoted, but the above may suffice to illustrate the general characters and mode of occurrence of the genus. It is important that the student should become familiar with the _Lithothamnion_ and _Lithophyllum_ types of thallus, in view of their frequent occurrence in crystalline limestone rocks and in such comparatively recent deposits as those of upraised coral-reefs. The coral-rock of Barbados and other West-Indian islands affords a good illustration of the manner of occurrence of fossil coralline algae in association with corals and other organisms[361]. In the fossil species of _Lithothamnion_ hitherto recorded there do not appear to be any important features in which they differ from recent forms; the geological history of the genus so far as it is known, favours the view that the generic characters are of considerable antiquity. _Solenopora._ Fig. 38. Mr A. Brown[362], of Aberdeen, has recently brought forward good evidence for including various calcareous fossils, described by several authors under different names and referred to various genera of fossil animals, in the genus _Solenopora_, which he places among the coralline algae. Species of this genus have been described from England, Scotland, Esthonia, Russia, and other countries. The geological range of _Solenopora_ appears to be from Ordovician to Jurassic rocks; in some cases it is an important constituent of beds of limestone. • • • • •