UNUSUAL FOKH OE HEMIPHOLIS. 139 



The mouth-shields are small and triangular in outline ; they 

 are about as long as broad, are pointed orally, and are outwardly 

 curved distally. Their position is very oblique ; and their free 

 surface passes downwards and inwards, so that the proximal end 

 is on a lower plane than the broad distal curve. The sides are 

 slightly incurved. 



The side mouth-shields are very small and narrow ; they do 

 not meet orally, and they are as long as about one half of the 

 side of the mouth-shield. Each supports a long and slender 

 spinule, which projects downwards and slightly outwards, and is 

 situated at the end of the inner third of the shield and ab- 

 orally to a large tentacular opening. The oral ends of the jaws 

 are close together, and are on a lower plane than the side mouth- 

 shields ; hence the jaws and the lowest true teeth project down- 

 wards. Their mutual contact forms a small pentagonal area with 

 curved edges, closed by the lower teeth ; and this is at the end 

 of a process which projects downwards in consequence of the 

 downward curving of the jaws. 



There are thus no true mouth-papilla?, and tooth-papilla? are 

 absent. The first tentacle-spine is not visible high up at the 

 side of the jaw, and the spaces between the jaw-angles are nearly 

 covered with a delicate skin. The lowest tooth of each jaw is 

 in close contact with its neighbours ; they are all on a level 

 plane and completely close the oral passage. The teeth are 

 triangular in outline. The spaces between the jaw-angles are 

 mere slits, and no tentacle passes through them. The first 

 tentacle is in the place occupied in other forms by the second 

 tentacle, and it is large and in relation to the spine on the 

 side mouth-shield. This spine, according to ordinary termino- 

 logy, would be a mouth-papilla, so that each angle has two of 



The arms, five in number, are unequal in size ; and there are 

 only two joints within the disk, but they are broad, and encroach 

 upon the interbrachial spaces. 



The first lower arm-plate is very small, and is faintly covered 

 with the extension of cellular skin ; and its shape is rather that 

 of a hatchet. The distal edge is the broadest, and is curved dis- 

 tally, whilst the inner or oral edge is narrow. The sides are 

 greatly incurved for the tentacular opening. The second plate, 

 small and about as broad as long, is broadest aborally, where it is 

 boldly curved. It is narrowest orally, where it is in relation to 



11* 



