122 THE CRAG POLYZOA. 



The cell-tubes in Heteropora, when traced internally, are seen to enter the branch at 

 first nearly horizontally, and gradually curving downwards, to descend vertically in the 

 centre of the branch, which thence comes to be occupied by a sort of pith, composed of 

 pretty nearly equal-sized, polygonal contiguous tubes. The interstitial canals rarely appear 

 to enter into this pith, usually terminating where the cell-tubes begin to assume the 

 perpendicular direction. In cases such as that of H. pustulosa (PI. XX, fig. 1, d), or of 

 Heteroporella radiata (PI. XIX, fig. 2, d), where the interstitial canals are of large size, 

 nearly equal in fact to the cells themselves, they may be distinguished from the latter by 

 their peculiar monilitbrm aspect, an appearance which is due to the existence of partial, 

 transverse, nearly equidistant septa. As it is not impossible that this peculiar condition 

 of the tubes might give rise to the mistaking of one of these Polyzoa for a true coral, 

 such as Favosites or Chaietes for instance, it will be as well to explain how it appears 

 to arise. In Heteroporella radiata, and in Heteropora pustulosa, and in other species 

 also, of what may be termed true Heteropora, the ostioles will often be found com- 

 pletely closed by a calcareous, depressed lid, which in the majority of cases, however, 

 is perforated in the middle. Now it would seeni that the imperfect septa above noticed 

 in the canals, represent the remains of these hymen-like lids, which have been left 

 behind at successive stages of growth. 



In //. clavata the interstitial orifices, or many of them, exhibit a stellate appearance, 

 owing to the projection into their interior of numerous minute rays ; affording thus another 

 curious, false resemblance to a true coral. This appearance, however, is not peculiar to 

 Heteropora, for a similar condition exists in the beautiful pores, for instance, which 

 ornament the front of the cells in Lepralia Mahisii, and may be observed in certain pores, 

 no doubt of exactly the same nature as those in Heteropora in at least one recent species 

 of Discoporella. 



The species furnished with these two kinds of orifices appear to be naturally divisible 

 into two groups, which may perhaps be regarded as generic, according as they are 

 encrusting or at least adnate, or massive, erect, and cylindrical. For the former I 

 venture to propose the term Heteroporella, n. g., and to restrict that of Heteropora to the 

 latter. 



1. HETEROPORA PUSTULOSA (n. sp.) ? PI. XX, fig. 1 ; PI. XIX, fig. 6. 



Irregulariter ramosti; ramis curvatis, teretibus. Orificiis peristomate incrassato, 

 quadrifido munitis et ostiolis 5 foveolatis circumcinctis ; tubulis interstitialibus, monili- 

 formibus, et in diametro ccllulis prope paribus. 



Polyzoarium branched irregularly ; branches curved, tapering ; cell-orifices with a 



