152 SIDNEY P. HAEMEE. 



been almost completely overlooked by all previous writers on 

 Crisia. The aperture is often said to be absent, as indeed it 

 may be in injured or abnormal ovicells. As will be seen from 

 a later communication, a normal ovicell is, according to my 

 observations, never without an aperture from the time when 

 the ovicell is first developed at the growing-point to the time 

 when embryos are ready to escape from the ovicell. The cal- 

 careous aperture is, however, throughout the development 

 closed by a thin cuticular membrane, and the presence of this 

 membrane sometimes makes it difficult to see the aperture in 

 those cases in which this structure is not borne on a distinct 

 tube. 



On breaking open an ovicell (fig. 10) it will be noticed that 

 the aperture leads into a space partially separated from the 

 rest of the ovicell by a valve-like structure of calcareous 

 nature. This valve has very definite relations to the structures 

 found in the interior of the ovicell, as will be described in my 

 subsequent paper. It springs from the posterior wall of the 

 ovicell, and passes obliquely forwards, being also attached to 

 the lateral walls of the ovicell in such a way as to leave a more 

 or less oval opening connecting the main cavity of the ovicell 

 with the aperture of the latter. The valve is most developed 

 at the back of the ovicell, and gradually dies away laterally as 

 it passes to the front wall of the ovicell, where it no longer 

 forms a distinct ridge. 



This valve is developed in all the four species which are 

 specially discussed in this paper, but it appears to be less well 

 developed in C. eburnea than in the other species. 



Note on C. cornuta, Linn., and C. geniculata, M.-Edw. 

 Until quite recently I had devoted no particular attention 

 to these forms, the specific identity of which appeared to be 

 perfectly established by such statements as those of Sraitt,^ to 

 the efi"ect that they may both occur as branches of the same 

 stem. But, having recently found some ovicells of C. geni- 

 culata, I cannot help believing that the two forms are speci- 

 > ' Ofvers.,' &c., 1865, No. 3, p. 128. 



