8 PATTEN AND REDENBAUGH. [Vol. XVI. 



ment to some of the plastro-coxal muscles of the sixth pair of legs, 

 which are the most powerful appendages of the animal. 



A marginal ridge is formed {in.r.. Fig. i) on the neural side 

 of the plastron, which becomes quite prominent anteriorly ; pos- 

 teriorly it dwindles to a low rounded shoulder at the base of the 

 latero-posterior process, then rises a little, to form the base of the 

 occipital ring {per., Figs, i, 3, and 4). There is also a shoulder 

 (j.. Fig. 4) running across the body of the plastron, connecting 

 the posterior borders of the latero-posterior processes. 



6. The posterior process {p.pr.. Figs. 1-4) begins as a thick- 

 ening on the haemal side of the plastron between the haemal 

 processes. It increases in thickness posteriorly, and ends in a 

 bifid process, each division of which is deeply grooved on the 

 haemal side. Along the whole haemal side of the process are at- 

 tached two large muscles going to the first pair of entapophyses. 



On the body of the plastron, on both sides of the base of the 

 posterior process, are attached longitudinal abdominal muscles, 

 passing backward between the last described muscles and the 

 plastron. The attachments of these muscles extend a little an- 

 terior to the haemal processes. In front of this the body of 

 the plastron is destitute of muscles on the haemal side. 



A pair of small chilarial muscles are attached to the haemal 

 side of the extremity of the posterior process. 



7. TJie capsuliginoiis bars {cap.b., Figs. 1-4) are a pair of 

 processes of peculiar structure arising from the posterior mar- 

 gin of the plastron, alongside the posterior process. The 

 latero-posterior process on each side is extended backwards as 

 a much thinner layer of cartilaginous tissue. It is flush with 

 the neural surface of the posterior process, but where it joins 

 the latero-posterior process there is a very abrupt shoulder 

 upon the neural side and a slight one upon the haemal side. 

 To the posterior margins of these thin portions are attached 

 the rod-like bars. The latter bend neurally and slightly 

 toward the median line, enter the bases of the chilaria, and are 

 attached to their posterior sides. 



A small transverse muscle joins the distal ends of the two 

 bars. Two other small muscles run to the chilaria from the 

 thin portions of the plastron near the bases of the bars. 



