176 Frederic/.- Cluvpiuaii : 



striate," but he does not luciitioii the i-adial striae seen in our 

 form. Judging from an examination of several hundred examples 

 of the calcareous internodal joints of Mopsea from the Mallee bores, 

 Tenison Woods' specimens may liave been abraded, so that the 

 fine, salient radii were cleared away, leaving only the more deeply- 

 marked concentric growth stages of the calcareous part of the 

 axis. Specimens in the present collection show both conditions. 



Description . — Calcai-eous joints forming the internodes, circular 

 to elliptical in transverse section ; short and wide when from the- 

 base of the coral; longer, to extremely slender and circular in 

 section where forming the nuiddle and distal joints. Sides straight 

 to incurved, and slightly dilated at the ends, especially in the 

 terminal joints; with numerous, fine linear ridges or striae. 

 Articular facets flat to C(niieal, with strong concentric rings of 

 growth and numerous fine radii. The concentric rings are undu- 

 late, and outwardly concave to meet the axial radii at the cusps. 

 The radii are in systems of eight, and these, with the concentric- 

 lines, produce a very ornate effect on the articular surface in well 

 preserved specimens. The stiiae of the cylinder coi'respond Avith the 

 radial lines of the condyles. 



Microscopic Structure of the CdlcdreouK Internodes. — A trans- 

 verse section of the joints shows that the axis is built on a system 

 of eight rays which send off secondary and tertiary branches; and 

 these consist of thin calcareous plates with a slight upward curva- 

 ture, giving a tegulate appearance to the rays, in section. The 

 inter-radial areas appear to be formed of fused, spicular bodies. 

 Compared with the structure of the calcareous axis in a living 

 Mopsea (M. cf. encrinula, Lamarck sp.V the fossil species here 

 described (M. tenisoni) shows fundamentally similar structure, 

 though on a coarser scale. This is probal)ly owing to the rays not 

 having advanced beyond the jirimitive eight. Tlie tegulate api)car- 

 auee is seen in both the living and fossil species. 



Dimensions of Calcareous Joints. — Three typical specimens were 

 selected. 



A. — Specimen of a basal joint ; 0x8 nmi. in diameter. 4 mm. 

 high. 



]{. — A median joint, that is, fiom the middk' liranelu's of the 

 coiiillum; 2.5 nmi. in diameter, T) nun. liigh. 



('. — A terminal joint; .75 mm. in diameter, 2.25 nun. high. 



JJisfribution.— Bore 1, 215-244 feet. Bore 3, 201-220 feet; 226 

 feel. Bore 4. 103-170 feet. Bore 8, 210-219 feet. Bore 9. 315-325 

 feet. Bore 10, 310-320 feet. Bore 11, 267-590 feet. 



