F. B. Longe — Oolitic Polyzoa. 23 



For lei P S Q be an orthogonal section of the surface whose ti-ace 

 is required. Draw B S inclined at an angle -v/r to F Q. Then B S 

 will be the direction in which the distortion in the trace will be 

 greatest. 



To delineate the trace, draw a horizontal line A C, and make 

 A C=P Q cosec a. 



Draw JSF making the angle ^ with A C. It is the direction of 

 greatest distortion. 



Divide P Q and A C into the same number of equal parts, and 

 draw ordinates parallel to B S and JIF respectively. Then, if the 

 ordinates on A G he made to bear to those on P Q the ratio of cosec 6 

 to unity, their ends, when joined by a curve drawn libera manu, will 

 give the trace desired. 



In the example (Fig. 2), it is supposed that the strike of the 

 cylinder, or folded surface, is N.E. by N. and S.W. by S. ; and that 

 the direction of the cutting plane is E. and W., and that it is inclined 

 at an angle 60° to the horizon. 



In this case a=SS° 45'', 

 and /3=60°. 



Our equations then give, 



1/^=34° 46', 

 j> =18° 28^ 

 6 =28° 45', 

 and the trace of the left-hand figure is sufficiently correctly de- 

 lineated by that on the right. 



For a railway cutting, 60° would be a very high angle. In the 

 case which we examined in Kent it was about 30°. This smaller 

 angle would impart a much greater obliquity to the trace. 



lY. — On the Eelation of the Eschakoid Forms of Oolitic 



Polyzoa to the Cheilostomata and Cyclostomata. 



By Francis D. Longe, F.G.S. 



(PLATE II.) 



THE Oolitic Polyzoa have been very little studied in this country. 

 They are badly represented in our museums, and no systematic 

 account of them has been given by any English writer. Their 

 remains, however, are both abundant and often well-preserved in 

 the Pea-grit beds of the Inferior Oolite near Cheltenham, and in the 

 Forest-marble beds near Bath. Some Inferior Oolite beds near 

 Metz, and the Forest-marble beds near Caen in Normandy, are still 

 more prolific, and the produce of these several beds has furnished a 

 very full illustration of the more prevalent forms of this class which 

 lived in the Oolitic seas. 



In comparing these forms with those of the living representatives 

 of the class, we observe that while the Oolitic group contains several 

 obsolete forms, two, at least, viz. the creeping Diastopora and 

 Alecto (Stomatopora) , have survived to the present time, retaining 

 their identitj^ in a very remarkable manner, both in respect of cell 

 features and habit of growth. Of these two forms, we are only 



