456 



PEOr. p. M. DUNCAN OF SOME 



is a sliglit sTioulder wliere tbe angular part joins on to the rest, on 

 either side, and it marks the line of contact, without, of the side 

 mouth-shield and the end of the wide generative opening. The 

 angular part is enclosed by the obliquely placed side mouth-shields, 

 which are joined within broadly, and which are rather swollen. 



The jaws form a short broad angle, and are rather swollen lon- 

 ' gitudinally close to the mouth-papillse. There are three small 

 spiniform mouth-papillae at the apex — one at the angle over the 

 teeth, and one on either side. The other papillae are long, low, 

 thin ridges, sometimes separated slightly into four indefinite 

 masses on either side, that nearest the spiniform teeth being 

 pointed. The papillae are small. There are five teeth, the upper- 

 most being the largest ; they are small, narrow, projecting, flat 

 and spear-headed. 



The upper arm-plates. — The first, seen close to the notch and 

 within the radial shields, is rudimentary. It is a broad, very short 

 lamina, with some rudimentary spinules upon it on either side. 

 The second is small, broader than long, curved without (re-enter- 

 ing), and tumid ; it carries spinules on its sides. The third, much 

 larger, and often the largest on the arm, is broader than long, 

 broadly heart-shaped, the broad rounded angle within being some- 

 times overlapped, and the large distal curve is produced to a slight 

 angle on either side. The seventh plate is pointed and angular 

 within, and much rounded without ; length and breadth nearly 

 equal ; and it is separated from the eighth by a slight median 

 union of the side arm-plate. At the end of the arm the upper 

 arm-plates are greatly separated, are broader than long, and heart- 

 shaped, forming a minute prominence. The plates near the base 

 of the arm are swollen, especially distally, and the surface is 

 marked by minute radiating lines. 



The under arm-plates. — The first is about as long as broad, 

 smallest and bluntly angular within, largest and re-enteringly 

 curved without, and more or less triangular, with the angles cut 

 ofi" or curved ; the centre of its surface projects slightly. The 

 second plate is larger, nearly square, with curved corners, nar- 

 rowest within, sloping at the sides, projecting in the middle, and 

 marked with short furrows ; its proximal edge is slightly curved 

 towards the disk, and the edge, without, has a very faint notch 

 and a broad shallow re-entering curve. The third plate, squarish, 

 is broadest without, and the next has a very decided distal curve. 

 All project and are marked at the sides. The eighth is small, 



