226 PORINID^. 



Family XII. — Porinidse (part.), D'OrUgny. 



MEMBEANiPORiDiE (part.), Busk. 

 EscHARiPORiD^ (part. ), Smitt. 



ZoARiUM incrusting, or erect and ramified. Zocecia ivith 

 a raised tubular or subtubular orifice, and frequently 

 a special pore on the front wall. 



It is difficult to determine how far division and sub- 

 division should be carried in classification. The present 

 family has many points of affinity with the preceding ; and 

 it may fairly be a question whether it is better to separate 

 the two on the ground of their differences, or to blend 

 them for the sake of their agreement. 



On the whole (though not without doubt) I am inclined 

 to keep them apart^ taking the tubular prolongation of 

 the cell above^ with its terminal and usually orbicular 

 orifice, as the chief characteristic of the present group ; 

 in the more typical forms we have also the special pore 

 on the front wall*. Amongst the Microporellidee the 

 mouth of the cell is either semicircular or exhibits a mo- 

 dification of this form_, the lower margin being always 

 straight or nearly so. It is never elevated on a free 

 tubular extension of the cell-wall. In the present family 

 there is a certain indefiniteness in the degree in which the 

 oi'al extremity of the zocecia is developed ; but the adult 

 cell is always more or less lageniform. 



The special pores amongst the Porinidce seem to be of 

 simple structure, and destitute of the protective contri- 

 vances which occur so commonly in those of the preceding 

 family. 



* In the aberrant genus iMgcnipora it is wanting ; but the zocecia are so 

 essentially Porinidan that it naturally finds a place in this family. 



