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NEW YORK STATE MUSEUM 



arrangement throughout the whole thallus such as this form 

 possesses is, however, not observed among the coralline algae 

 which for the most part possess only a flat, incrusting thallus and 

 in the erect forms, as in Corallina, are bifurcating or irregularly 

 branching, mostly in but one plane. The habitus of Primicorallina 

 as restored in this publication [see pi. i, fig. 2], is distinctly that 

 of one of the verticillate Siphoneae and well comparable to that of 

 Dasycladus or Polyphysa and other genera of the Dasycladaceae. 

 Since calcification takes place also in several of the genera of this 

 order of algae, and other calcareous verticillate Siphoneae were 

 already abundant in the Lower Siluric seas, as shown by Stolley, 

 it is preferable to place Primicorallina with the verticillate 

 Siphoneae. 



A reference of Primicorallina to the Dasycladaceae invites com- 

 parison to the other verticillate Siphoneae described by Stolley 

 from the Swedish Lower Siluric. The latter forms differ in having 

 the branchlets incrusted like the recent calcareous genera of Dasy- 

 cladaceae (Cymopolia, Bornetella and Neomeris), to such an ex- 

 tent that a solid cylindric mantle is formed in which the branch- 

 lets are imbedded. In Primicorallina the incrustation of the axial 

 cell and of the branchlets is comparatively slight, so that all the 

 branchlets remain free. This is obviously only a difference in grade 

 of calcification. Another difference rests seemingly in the segmen- 

 tation of the stem which suggests a composition of the stem of 

 more than one cell while in the verticillate Siphoneae it consists of 

 but one, the axial cell. Cut it is here to be remembered that on 

 one hand the axial canal in Primicorallina shows no or but little 

 contraction (as far as can be seen from the few type specimens 

 without breaking them) at the articulations and may well result 

 from a single axial cell and that, on the other hand, an articulation 

 of the whole thallus without subdivision of the axial cell exists 

 also in the recent Cymopolia. 



From Arthroporella Stolley, which consists of a chain of spheric 

 and pear-shaped bodies such as the branchlets of Primicorallina 

 might also form when seen in sections, the latter genus differs in 

 having these bodies articulate while in Arthroporella the incrusta- 

 tion is continuous and is also distinctly porous. 



It is very probable that Primicorallina has not only interest as 

 one of the earliest known calcareous verticillate Siphoneae but that 

 it is also of importance in explaining the origin of certain Trenton 

 limestones of granular and oolitic texture. Small grains which 



