290 Prof. H. A. Nicholson — On a New Silurian Coral. 



(2.) A certain number of the corallites may have their visceral 

 chambers definitely circumscribed ; but others are united in serial 

 rows by deficiency of their walls on corresponding sides. These 

 rows are sinuous ; and the calices assume, therefore, largely the form 

 of winding labyrinthine grooves (PL VIII. Fig. 2). 



(3.) No septa or septal spines are present. In examining the 

 surface of well-preserved specimens one might be easily led to sup- 

 pose that irregular septa were here and there developed ; but these 

 apparent septa are really only the inward projections of the walls of 

 the corallites marking the boundaries of the separate tubes in the 

 serially united rows. 



(4.) In the completely circumscribed corallites, the tabulae are 

 simple, and are either horizontal or are curved with their convexities 

 pointing towards the calices. On the other hand, in the serially 

 united corallites the tabulas become vesicular by reason of their con- 

 fluence in adjoining tubes. 



(5.) The mode of increase is by fission of the old tubes. 



The characters above enumerated form, as before remarked, a com- 

 bination so peculiar, as to render it impossible to refer the specimens 

 possessing them to any recognized genus of the Favositidas. I there- 

 fore propose for their reception the new genus Desmidopora. The 

 essential distinction between this genus and all the normal genera of 

 the Favositidaa is the fact that in Desmidopora the mode of growth is 

 fissiparous, and that many of the corallites are thus confluent in 

 serial rows. Apart, however, from this fundamental distinction, 

 there are minor features which separate the present type from the 

 normal genera of the Favositidse. Thus, in Favosites itself there is 

 a persistent primordial wall to the corallites, and septal spines are 

 usually present ; whereas in Desmidopora the walls of adjoining 

 tubes are indistinguishably fused together, and no traces of septal 

 structures can be detected. In Pachypora, Lindstr., again, not only is 

 there a persistent primordial wall to the corallites, but each visceral 

 chamber is contracted by the development of a special secondary lining 

 of sclerenchyma. The genus Alveolites, Lam., is separated by the 

 minor peculiarities of the oblique form of the calices and the presence 

 of septal teeth or ridges, while the mural pores are large and 

 uniserial. Lastly, the genus Laceripora, Eichw., makes a nearer 

 approach to the present type than is the case with any other known 

 genus of the Favositidee. Apart, however, from the fundamental 

 point of the fissiparous mode of increase in Desmidopora, the genus 

 Laceripora, Eichw., is further separated from the latter by the per- 

 sistent primordial wall of the corallites, the possession of distinct 

 septa, and the fact that a special secondary lining of sclerenchyma is 

 developed in the tubes in the peripheral region of the corallum. In 

 tangential sections of Laceripora the visceral chambers of adjoining 

 tubes often become connected by deficiency of the intervening wall ; 

 but this is not due — as might easily be imagined — to fission of the 

 tubes. On the contrary, it is simply due to the fact that the section 

 happens to cut at such points across the very large mural pores with 

 which the corallites are provided. 



