riSTFLOSE POLTMOEPHIN"^, AJTD ttEITUS EAMULIITA.. 497 



These admit of being grouped as follow : — 



I. Apical. — Those which have the exogenous shell-growth 



confined to the apical or oral extremity of the shell 



(apical) : and of this kind there are five recognizable 

 varieties, namely, — 



1. Single crest. A simple comb or crest with marginal 



tubes. 



2. Circular and flat. A flat circular top with marginal 



tubes. 



3. Badiate cushion. Tubes radiating from a cushion-like 



mass. 



4. Badiate cluster. Radiate or subradiate cluster of tubes. 



5. Bacemose. An irregular fistulose mass. 



II. Subapical. — Those in which the fistulose outgrowths are 



confined to the region just below the apertural apex. 



III. On tlie general surface. — Those which have either tubes 

 or irregular fistulose patches scattered on the general 

 surface. 



• IV. Marginal. — Those in which the extra shell-matter is 

 arranged as a thin outstanding flange or wing on the 

 margin. — Most of these last were perhaps parasitic, 

 attached to some object. 

 y. Mixed. — There are many specimens which combine more 

 or less of the foregoing kinds of outgrowths, — thus 

 apical, subapical, on the general surface, and on the sides 

 or the margin ; and therefore they cannot stand as 

 specially separate varieties. 



I, 1-5. — The first four groups of the apical growths seem to 

 keep tolerably separate from the others in being confined to the 

 apical region, and do not occur in the mixed forms ; but the 

 racemose style of outgrowth is variously modified in the general- 

 surface, marginal, and mixed groups. 



II. Sulapical growths. — The examples of the subapical or 

 cervical arrangement of tubules or fistulsa are not common as a 

 distinct group. They consist in one case (39*) of coarse tubes 



* These numbers refer to the detailed catalogue at pp. 508-516. 

 LINN. JOFEN. — ZOOLOGY, YOL. IXV. 41 



