BRYOZOA. 627 



S. decipiens, having the number of branches increase mainly by 

 bifurcation; the second, containg S. biserialis, S. biserialis var. 

 nervata, S. pinnata,S. robusta,S. robusta var. intermedia, and S. 

 delicatula, having the number increase entirely by interpolation. 

 The first group is, so far as known, only represented in the 

 Chester group, while the second, though occasionally met with 

 in those beds, is almost restricted to the Upper and Lower Coal 

 Measures. The discovery of this fact aided greatly in the sepa- 

 ration of the species. 



The position of the genus is between Pinnatopora Vine and 

 Synocladia King. Both Meek and Swallow regarded S. biseri- 

 alis as a species of Synocladia, but that they were in error is 

 now generally admitted. S. virgulacea King, the type of that 

 genus, has from three to five ranges of zocecia, and, so far as 

 known, is without the small accessory pores which are so char- 

 acteristic of all the species of Septopora. The relations to 

 Pinnatopora, though very evident, have not heretofore been 

 pointed out. Take for instance S. decipiens, and we find upon 

 comparison with species of Pinnatopora, that the only im- 

 portant character not common to them are the accessory pores. 

 The importance of even this distinction is diminished by the 

 discovery of similar pores on the reverse of Pinnatopora tiexu- 

 osa. All the remaining species of Septopora form a fenestrated 

 expansion by the union of the pinnae of neighboring branches. 

 The appearance of the ordinary zoarium of the two genera is. 

 therefore, quite different, but, here again, P. sedgwicki Shrub- 

 sole, lessens the utility of the difference, being likewise possessed 

 of a fenestrated zoarium. Certain differences in the internal 

 structure of species of -these two genera may be noticed in 

 comparing the figures on PI. LVI. S. robusta, in having three 

 ranges of zooecia on the pinnee, or as they are usually called, the 

 poriferous dissepiments, approaches Acanthocladia and Syno- 

 cladia, two genera that hold the same relations to each other 

 as Pinnatopora and Septopora. 



