55 
_.. Asapaus Prevrorryx.* . Cast No. 18. wins 
_Corpore depresso; cute coriacea tuberculis mini- 
‘mis; costis striatis; cauda acuta, brevl. 
~ This species like most other specimens of this 
genus, in our cabinets, is decapitated—every other 
part, however, appears to be in a goue state of pre: 
servation. . ; 
The articulations of the abdomen and tail, which 
cannot readily be distinguished from each other, are 
seventeen in number. The middle lobe is flat, and 
regularly tapers to an obtuse lip; it is marked on 
each side with longitudinal impressed lines or little 
grooves, The costal arches on their upper side have 
a deep and narrow channel, running through their 
whole course. The costal arches of the abdomen 
have no membranaceous expansion beyond their ter- 
minations; this organization is only visible immedi- 
ately below the end of the middle lobe, where it quick- 
ly finishes in an acute point. A large portion of the 
crustaceous shell remains, and is covered with dis- 
tinct granulations; those on the tail are the least 
obvious. | tie 
This species approaches very near the A. caudatus, 
| but the grooves on the middle lobe, the smallness of 
the costal arches, and the limited extent of the mem- 
branaceous expansion round. the lower portions of 
the shell, will sufficiently distinguish it. 
_* From the Greek word for “ grooved ribs.” 
