TRIBE DIASPIDINI 301 



caudal margins are convex. The lateral margins are slightly 

 convex and are rarely if ever almost straight and converge caudad. 

 The mesal part of the caudal margin of the pygidium in a num- 

 ber of species is concave or emarginate and provided with a pygi- 

 dial incision. This is variously described as a deep median cleft 

 or the pygidium as semicircularly hollowed out. 



The lobes vary in number as in the other tribes. There are 

 typically about three pairs, the median pair is always the largest. 

 The second or third pairs may be divided into two or three lobe- 

 lets or deeply incised. When the caudal margin of the pygidium 

 is concave or provided with a pygidial incision, the first pair of 

 lobes is usually located in the concavity, oblique in position and 

 the greater part of their lateral margin is continuous with or 

 fused to the pygidium. Their mesal margins, which are usually 

 convexly rounded and continuous with the rounded distal ends, 

 are usually finely serrate or crenulate. Where the median pair 

 of lobes is free on the lateral margin, their distal ends are 

 usually notched. In certain species the proximal ends of the 

 median lobes are fused, in others their mesal margins are straight 

 and adjacent, the two lobes appearing to form a single semicircu- 

 lar area, while in others the adjacent mesal margins have fused 

 until there is only a notch on the meson marking their point of 

 separation. The margins of the second and third pairs of lobes 

 may be serrate, crenulate, or notched, if notched, the number 

 and distinctness of the notches vary with the species. In a few 

 species all the lobes have been lost and the margin of the pygidium 

 is entire, in some others pseudolobes which are very lobe-like in 

 appearance have replaced the true lobes. 



The plates are only rarely wanting except in the median in- 

 cisura where they are only rarely present. They are usually long 

 and slender, as long as or longer than the lobes, spine-like in form, 

 with lamaceratubae opening in their pointed ends. The plates 

 are usually arranged, 0, 2, 2, 2, 2, or 0, 1, 1, 1,2. There is not 

 much variation in the number in the different incisurae and on the 

 lateris. The plates are in extreme cases represented by apically 

 furcate furcapectinae. The group of four or five plates near the 

 cephalic end of the pygidium is located on the caudal segment of 

 the preabdomen. 



The altaceratubae are prominent, large with comparatively 

 long tubes. They are generally located singly but in some species 



