268 Proceedings of the Royal Irish Academy. 



from the bare tracts. Transversely, four or five is a common number in 

 each series. 



2. Juncclla trilineata. — The polyps are arranged in transverse rows of 

 three to four, but many smaller polyps occur which break this regularity. 

 For a short distance from the ends of the branches the polyps occur in three 

 single rows ; but passing downwards two, three, four, or more are to be seen, 

 and, scattered amongst these, are immature forms, so that all that may be 

 said with regard to the disposition of the verrucae is that they occur in three 

 longitudinal groups. The exact number in a transverse row depends on the 

 position in the colony and on the stage of development. The three 

 longitudinal series are separated by three distinct bare tracts. 



3. Sdrpearia quadrilincata. — The polyps are grouped in four definite 

 longitudinal series separated by four bare spaces which correspond in position 

 to tlic four main canals. Eacli series consists of a single row; but near the 

 niiiidle of the colony they are somewhat crowded, and give an appearance of 

 two rows, due, in gieat part, to displacement and the interpolation of young 

 polyps. 



From these descriptions the following conclusions will be at once 

 evident : — 



(1) The polyps are always arranged in a certain number of longitudinal 

 series which are definite for the species. 



(2) This number is dependent on and is the same as the number of 

 longitudinal main canals. 



(3) The number of transverse rows in each series may vary according to 

 the position in the colony, so that no definite number can be regarded as 

 specific. 



(4) Tiie number of rows generally increases in the older parts. 



(5) This is due to the iutcqxilation of young polyps. 



(6) Near the Iwise of a colony the different series may so approximate, 

 owing to overcrowding, as to abnost obliterate the bare tracts. 



(7) This may result in a spiral appearance wluch is not inherent, but 

 secondarily produced. 



(8) A similar false spiral appearance may be produced by a torsion of the 

 whole colony. 



We have now reached a point when it is necessary to ascertain to what 

 extent the distribution of the verrucae may be regarded as of taxonomic 

 importance. 



The question of a spiral arrangement is certainly inadmissible, as is also 

 the number of transverse rows in any seriee ; so that to us it seems that the 



