6 if Stability of Structures in regard to Wind-Fressure. 



strength of wroiight-iron is taken at 20 tons per square 

 inch. 



Breaking Weights of Different Parts. 



Bar by tension 

 Bar by shearing of end ... 

 Bolt by shearing at centre 

 Gusset-plates, shearing by bolt ... 

 Gusset-plates, shearing by rivets 

 Rivets by shearing 



... 60 tons 



... 75 tons 



... 91 tons 



... 120 tons 



... 120 tons 



... 25 tons 



In altered Position of Plates, 

 Rivets by shearing ... ... ... 50 tons 



In the next paper I hope to treat of the wind-pressure 

 upon roofs, in connection with which I have been making 

 experiments. 



Art. VIII. — Descriptions of Neiu, or Little Known, 

 Polyzoa. 



Part XI. 



By p. H. MacGillivray, M.A, M.R.C.S., F.L.S. 



[Read 8th July, 1886.] 



Family Catenicellid^. 



Catenicella gemella, n. sp. Plate I., fig 1. 



Each internode consisting of a geminate pair of zooecia,, 

 each pair in the main stem giving origin to two double 

 zooecia, the one pair continuing the stem directly upwards, 

 the other originating a lateral branch, these branches start- 

 ing alternately right and left; the lateral branches mostly 

 undivided, but occasionally giving off secondary branches;, 

 in the lateral branches, the geminate pairs giving off the 

 next pair alternately from the right and left zocecium;. 



