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cases with a zisfzasf keel on its frontal surface. Ooeciostome in contact with a median zooecium, 

 which it resembles; the ooeciopore not differing much from a zooecial orifice and facing more 

 or less distally. The stalk of the colony becomes cylindrical by the development of a secondary 

 cancellated growth on its basal surface. 



This delicate species has a considerable resemblance to Crisina radians in external 

 appearance; but differs from it in many important characters. The younger branches are 

 narrow and strap-like, as seen in basal view; and are without cancelli. In nearly all the 

 specimens referred to this species, the basal surface is marked by ripple-like lines of growth 

 (fig. 4). The ripple, which is slightly elevated, is convex distally, and the pores of this surface 

 of the branch are generally arranged in a single series along the projecting part. This character 

 is somewhat variable, but in several of the specimens it is an extremely pronounced feature. 

 The basal surface is nearly fiat, but is usually slightly concave; and it is separated from the 

 lateral surfaces of the branch by a sharply marked edge. In the main stalk of the colony this 

 arrangement becomes modified by the superposition, on the original basal surface, of a secondary 

 thickening, which grows in a distal direction, but does not extend far up the colony. This 

 thickening, which has a cancellated structure and is shown in fig. 4, corresponds with the "canaux 

 de renforcement" which have been described by Pergens : ) in species of Idmonea. 



The frontal surface of the branch is most elevated at its middle, owing to the fact that 

 the more median zooecia are much the most prominent. The zooecia, which are closely connate 

 in each series, are usually four in a series, but sometimes five or even three or two. The median 

 zooecium may project beyond its neighbour, and thus have a free peristome. The orifices are 

 nearly circular. The colony may commence with one or two alternating single zooecia; a 

 bi-zooecial condition next following and the full number being quickly acquired. 



The ovicell constitutes a specially characteristic feature of the present species. Its length 

 varies with the degree of vigour in the growth of the colony. In most cases it is very long, 

 corresponding in length with as many as 1 2 series of zooecia of one side. Near its frontal part 

 it is somewhat compressed, in such a way as to form a zigzag keel, giving off a branch to 

 each series of zooecia, as indicated in fig. 5. Evidence that it is morphologically a modified 

 median zooecium is given by two facts: — (I) it commences proximally with a narrow portion 

 which occupies the position of a median zooecium; (II) the ooeciostome (fig. 5,0) occurs on the 

 median side of one of the series of zooecia in the course of the ovicell. From the fact that the 

 ooeciostome has a considerable resemblance to an ordinary peristome it is not very conspicuous; 

 and since only one ooeciostome occurs in each ovicell, the inner edge of a number of series 

 may have to be examined before it is discovered. The carinate condition of the ovicell is usually 

 well marked, but in some specimens it is hardly apparent. The ovicell generally commences 

 a short distance on the proximal side of a bifurcation, and forks with the branch; sometimes 

 bifurcating a second time when the branch divides. 



The specimens 459. H. and 394. O. are rather more robust than the others. The basal 

 surface has rounded edges and the pores are uniformly scattered, without being confined to 



1) Pergens, E., 1S90, "Rev. Bry. Ciétacé", Buil. Soc. Beige Géol., III, p. 311. text-fig. 5 (p. 312); cf. also Kirkpatrick, 

 1888, «Pol. Mauritius", Ann. Mag. Nat. Hist. (6) I, PI. X, fig. ■>!> [Idmonea tortuosd). 



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