a General History of the u* t 3 Polyzoa. 379 



ribs pass off to the margin, so as to enclose a triangular 

 space. 



Loc. Mediterranean or Red Sea (R. 8. Newall). 



This form seems to be a variety of M. coriacea, distinguished 

 by the total absence of the nodulous enlargement of the 

 margin on each side immediately below the orifice. This 

 character can hardly be accounted of much importance, as it 

 is one of those which are found to be liable to great variation. 

 I have not noticed avicularia on the present form ; but they 

 are often wanting on the normal M. coriacea. 



Steganoporella, Smitt. 



Steganoporella Rozieri, Audouin. 



This species was figured by Savigny in his work on Egypt ; 

 and subsequently by Busk in his ' Catalogue,' from speci- 

 mens obtained by Mr. Darwin in South America. It occurs 

 in various parts of the world, but with certain modifications, 

 which are extremely interesting as illustrating the range of 

 variation and indicating the elements of structure which are 

 most liable to change. 



In the normal S. Rozieri the raised margin terminates 

 above on each side in " a small tuberosity," and the front of 

 the cell is represented as decidedly elliptical ; avicularia 

 are altogether wanting; the ooecium is large, globose, and 

 somewhat bilobate. 



In Mazatlan a form occurs (described by Busk as a species 

 under the name Membranipora gothica*) which seems to be dis- 

 tinguished from the foregoing chiefly by the non-development 

 of ooecia and the presence of large avicularia. The ooecium 

 (according to Busk) is " represented by one or two rounded 

 eminences at the bottom of the cell in front." This variety 

 is very abundant at Santa Monica, California, where it spreads 

 profusely over weed • I have figured it from a specimen ob- 

 tained in this locality (PI. XVI. fig. 3). 



Another form has been received from India (PI. XVI. 

 figs. 1, la). In this the marginal tuberosities, which are so 

 conspicuous a character in the two preceding, are wanting ; 

 avicularia are present, which bear a general resemblance to 

 those of 8. gothica, Busk, though they are furnished, I 

 believe, with a somewhat different mandible ; and there is a 

 large bilobate ooecium, like that of the normal 8. Rozieri 

 (PL XVI. fig. la). 



Yet another variety has occurred, from Australia, which 



* Quart. Journ. Micr. Sc. 1856, pi. vii. figs. 5-7. 



27* 



