592 Canon A. M. Norman — Notes on the 



At the outset let me say that I consider that Hincks^s 

 M. armifera has nothing to do with C. Soph'up., with which 

 Waters has united it. It can at once be distinguished by 

 the avicularia on the sides of the oral openings which in the 

 former point downwards and outwjrds, and in the latter 

 point upwards and inwards. An examination of specimens 

 from many localities proves that this is an unvarying rule. 

 Secondly, let me add that, notwithstanding the presence of 

 these lateral avicularia in M. armifera, I am unable to 

 regard it as more than a very interesting Arctic form of 

 C. unicornis, Fleming. I arrive at this conclusion because 

 it resembles unicornis — and it alone among allies — in usually 

 possessing no pore-chambers ; in the form of the ocecium 

 and its surmounting avicularium ; in the presence sometimes 

 of a pair of lateral spines, of which one is of moderate length 

 and acutely pointed at the end, while that which is opposite 

 to it is immensely developed, of great length, and in the 

 form of a hollow tube. 



The peculiarity which at once distinguishes it from typical 

 C. unicornis is the presence of avicularia at the sides of the 

 oral opening (see Pi. XIII. figs. 10, 11) with the mandible 

 pointing downwards and outwards. Commonly these avicu- 

 laria are on each side : sometimes on one side only and on 

 the other a spine ; sometimes over considerable spaces, or a 

 whole polyzoary, they are altogether absent. I have never 

 seen both avicularia and both lateral spines developed on the 

 same zooecium; the former when present would seem to 

 supersede the latter. Besides the lateral pair of spines there 

 is, at each corner of the upper margin, a small spine, and 

 these spines often remain buried in the ooecium, in which 

 minute round holes (for the spines are hollow) seen at the 

 lower corners of the ooecium indicate their presence. The 

 ooecium is similar to that of C. unicornis, with a similar 

 arched rib in front ; and, as in that species, at the base of 

 the zooecium is an avicularium of considerable size and 

 pointed mandible; when the ooecium is developed this 

 avicularium is seen above and appears to be part of it. 

 Occasionally this avicularium attains immense size (see 

 Hincks's figure in his paper of 1892 and my figure, PI. XIII. 

 fig. II) . My specimen, which has these very large avicularia, 

 is from Torske Bank, West Greenland, and all the avicularia 

 over the zoarium are of the same abnormal size. Now it is 

 curious that this zoarium should have been found on a large 

 valve of Pecten islandicus, and that on the other parts of the 

 same valve were two other zoaria of the same species, on 

 which the ooecia were of the normal dimensions (PI. XIII. 



