404 Mr. H. J. Carter on 



EXPLANATION OF THE PLATES. 



Plate XII. 



Farrea occa, skeleton of. From a photograph, about the natural size, of 

 the specimen. 



N.B. — The round black points represent the polypites of a parasitic 

 Hydroid. 



Plate XIII. 



N.B.— Figs 1-6 are drawn to the scale of l-24th to 1-lSOOth inch, to 

 show tbeir relative proportions. The rest are, for the most part, more 

 magnified views of the same, to show their detail. 



Fig. 1. Farrea occa, fragment of skeletal fibre from the upper part of the 

 specimen, a a a a, main fibre ; b b, spurs, whose punctate sur- 

 face is intended to indicate that they are for the most part 

 covered with short spines; cc, ends of spurs supposed to have 

 been broken off close to the base. 



Fin. 2. The same. Fragment of skeletal fibre from the base of the speci- 

 men, showing — a, fibre ; bb, small sexradiates. 



Fig. 3. The same. The barbula, on whose surface the spines of the 

 upper third only are represented. 



Fig. 4. The same. The dermal sexradiate. a, microspined form ; b, 

 maerospined form. 



Fig. 5. The same. The clavulce, in situ. 



Fig. 6. The same. The rosette. 



Fig. 7. The same. A series of more magnified views of the head and shaft 

 of the clavula, to show its transitionary conditions from a, the 

 simple, smooth, club-shaped, ovular form, to b, enlargement of 

 the upper part of the inflation, incipient tubercle on the summit, 

 and incipient row of spines across the body ; c, development of 

 tubercle into an umbo and the row of spines into a coronal 

 form projecting beyond the surface of the body ; inflation be- 

 comes constricted just below the crown, and the lower part 

 roughened by spines, which often present a subsidiary coronal 

 arrangement above ; d, the umbo disappears, leaving a smooth, 

 convex, dome-shaped summit, the coronal spines decreased in 

 number but increased in size, the constriction between the two 

 parts of the inflation increased and the spines on the lower por- 

 tion gone ; e, the coronal row of spines reduced in number to 

 four, which are much increased in size and situated at the car- 

 dinal points of the upper part of the inflation, which, in this 

 view, is seen to be devoted to their support or to the head, 

 while the constriction which separates it from the lower part 

 of the inflation that passes into the shaft is still more pro- 

 nounced ; /, the lower two thirds of the shaft, magnified upon 

 the same scale, to show its terminal but pointed inflation and 

 spinous surface. (AH these representations are magnified to the 

 scale of l-12th to l-0000th inch, to show their relative propor- 

 tions. ) 

 Fia. 8. The same. Fragment of the barbula, much magnified, to show 



the form and arrangement of its spines. 

 Fig. 9. The same. More magnified view of the rosette, showing the two 



