694 Proceedings of the Royal Irish Academy. 



furnislied. with three antennge, one on the occipital and two in 

 the lumbar regions. The first of these, which is very much th& 

 largest, has a peculiar structure. It is shaped something like an 

 adder's head, the two lips of which open to emit two long and 

 several shorter setae, and close again when these setae are retracted.- 

 The two small lumbar antenna are also dorsal in position, and 

 just penetrate the dorsal plate. An occipital eye is present, 

 large and bright red. The corona is formed of three cushion-like 

 lobes, clothed with long vibratile cilia in fan-like tufts. The 

 jaws are large and powerful. Of these characters, the chief and 

 most peculiar is the pair of articulated spines, which can be pro- 

 jected outwards and folded up by a pair of muscles at the will 

 of the animal. These spines are undoubtedly organs of defence, 

 for the creature is observed to extend them on the least approach 

 of danger. The muscles and the nature of the joint are best 

 observed when an individual is secured in a compressorium and 

 examined under a power of 250 or 300 diameters, the irritation 

 caused by the cover-glass inducing the animal continually to> 

 extend and retract the spines. The hinge at the base of the 

 spine seems to be a ball-and-socket joint ; it is fitted into an 

 indented recess on each side of the dorsal plate, and may be 

 readily observed either when folded or extended under a sufiicient 

 magnifying power. N. spinifer has a large stomach, usually 

 filled with brown matter, the colour of course depending on 

 the nature of the food within the creature's reach. The food 

 consists of both animal and vegetable organisms, chiefly Infu- 

 sorians, spores, and antherozoids of Algae. The head is pro- 

 jected a considerable distance beyond the front of the lorica, and 

 this circumstance, together with the presence of the long vibratile 

 cilia fringing the corona, enables it to be a vigorous swimmer. 

 The head is contracted swiftly within the lorica on the approach 

 of danger, at the same instant that the lateral spines are pro- 

 jected ; with its head drawn within the lorica, the creature is 

 then protected both by the six frontal and by the two lateral 

 spines. If the animal be kept in clear, filtered water, it becomes 

 very transparent ; the lateral tubes and vibratile tags may then 

 be easily observed, leading into an ample contractile vesicle, 

 which empties and fills twice in a minute. The animal deposits 

 its eggs at the bottom of the water, or on confervoid plants. 

 Length of adult -gV inch. I am indebted to Mr. Dixon-Nuttall 

 for the drawings which illustrate this description ; they are taken 



