17 
torily made out. The costal arches are, therefore, 
more numerous than the vertebral joints ; an organi- 
zation not very uncommon with the Asaphs. The 
first eight ribs and vertebrze, as seen in this fragment, 
appear to have been articulated together ; after which 
this irregular. structure commences. ‘The costal 
arches are rounded on their upper surface, without 
strize, broadest near. their lateral extreml 1eS, and 
are, most of them, irregularly nodulous 5 : 
dules resemble very much the abetting on the 
ribs of the Pecfen nodosus. The joints of the middle 
lobe are also reunded and nodulous, but on these the 
nodules are disposed in the form of two very obtuse 
para |. ‘logiams. “What renders this fragment pecu- 
liarly cee. is that the lower portion of the up- 
ng one of the lateral edves near the tail, 
is sO 
ends of the ribs which have here scaled off. At first 
) actured as to present the structure beneath the 
| sight the broad smooth edging round this part of the 
- fossil, resembles very much the membranaceous ex- 
pansion beyond the lateral lobes which is one of Pro- 
fessor Brongniart’s generic characters of the Asaph. 
This border indeed is very like the hem so strikingly 
exhibited in the Asaphus micrurus ; but upon com- 
paring the ribs on the opposite side, where they are— 
perfect, with those terminated by the border, it will . 
be seen that they are much longer ; what, therefore, — 
seems to be an expansion beyond the ends of the ribs 
in that place must be occasioned by the reflection of 
Q* 
