94 LOWER PENINSULA. 



development of these foveae, justly remarks that if only one of the 

 four foveae is well developed, it is always the apertural fovea which 

 he QaWs principal fovea ; but he is in error when he adds, " only in rare 

 instances the opposite fovea is best developed." This case never 

 happens ; in symmetrically curved, horn-shaped polyp cells the aper- 

 tural fovea is either in the median line of the convexity of the 

 curve or on the concave side. Not unfrequently the largest fovea 

 is found in a lateral position with respect to the curvature of the 

 polyp cells. But even if we find the largest fovea in such lateral 

 position, it does not follow that one of the lateral fovese has been 

 developed in preference to the others ; on close examination, it 

 will always be found that the septal striae on the surface converge 

 from both sides toward the median line of that fovea, which un- 

 mistakably proves it to be the apertural fovea ; if it were the late- 

 ral fovea the striae would converge toward it only from one side, 

 or if the central, they would be all parallel, which is never observed. 



Milne-Edwards divides the Zoantharia rugosa into four families: 

 the Stauridae, Cyathaxonidae, Cyathophyllidae, and Cystiphyllidae. 

 These sub-divisions, however, are artificial, not being based on 

 important differences in the plan of structure, 



StaiiridcB are described as polyp cells with well-developed, radial 

 lamellae, which intersect the whole length of the corallum as unin- 

 terrupted, vertical leaves, which are at intervals connected by short, 

 interstitial, transverse leaflets. The lamellae are grouped in four 

 fascicles, which have their limits'marked by very obvious septal gaps 

 visible within the'cells under the form of a four-armed cross. The 

 enumerated genera of Stauridae are : Stauria, a Silurian coral ; 

 Metriophyllum, a Devonian form ; Polyccelia, of Permian age. 

 No coral which could be identified as belonging to one of these 

 genera has been found in Michigan. 



Cyathaxonidce are described as single polyp cells, with well-de- 

 veloped radial lamellae, extending as uninterrupted leaves through 

 the whole length of the corallum, and uniting in the centre into a 

 cristiform columella. The interstices between the lamellae are 

 said to be open throughout without diaphragms or transverse, inter- 

 stitial leaflets. This family characteristic is based on imperfect 

 observation. The lamellae do not unite in the centre into a cristi- 

 form columella, and their interstices are not open all their length, 

 but have transverse leaves intersecting them, the conically protrud- 



