PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 347 



which become successively more remote posteriorly. There is a slight 

 median carina extending the whole length of the carapax, and armed, 

 behind the two rostral spines, first Avith a single small spine directed 

 forward, then with two, side by side and very close together, then with 

 one, then with two on the posterior edge of the cervical suture, then 

 with two more, and finally with two somewhat larger and more widely 

 separated spines projecting forward from the anterior edge of the broad 

 and prominently raised jjosterior margin. In front of the cervical 

 suture there is an irregular longitudinal dorsolateral line of five minute 

 spines each side, and back of these a single spine each side on the pos- 

 terior edge of the cervical suture. Extending from the posterior margin 

 nearly to the cervical suture, there is a sharp sublateral carina parallel 

 to the lateral margin, about a third of the way from it to the median 

 carina, and armed with five small spines on one side and six on the 

 other. The extra spine is on the left side, and next to the last in the 

 series, but is accidentally omitted in figure 5. 



The ventral regions of the carapax are inflected each side at a very 

 acute angle with the dorsal surface, and, the sternum being narrow in 

 front, the ventral regions are very broad in the middle, being broadest 

 opposite the bases of the first and second perteopods. The ventral 

 region each side is divided longitudinally into three approximately equal 

 parts by two prominent carinse; the outer carina (marking the pleuro- 

 tergal suture?) extends from the anterior margin at the base of the an- 

 tenna, in a slightly sinuous line, toward the posterolateral margin of 

 the carapax ; the anterior half is very prominent and armed with nu- 

 merous small spines directed outward, while the posterior half is much 

 less conspicuous, unarmed, and disappears entirely before reaching the 

 posterior angle of the carapax. The inner carina extends along the 

 branchial region from near the base of the first per^eopod quite to 

 the postero-lateral angle of the carapax ; the extreme anterior portion 

 is not prominent, but from opposite the third perseopod posteriorly it is 

 very prominent, acute, and armed with ten to fifteen sharp spines. The 

 outer of the three longitudinal regions thus marked out is divided trans- 

 versely by the cervical suture, and the anterior portion (subhei)atic 

 region) is divided transversely into an anterior and a posterior lobe by a 

 groove nearly or quite as conspicuous as the cervical. In the frontal 

 margin of this anterior lobe (figure 2), aud near its inner side, there is 

 a deep sinus corresponding to the orbital sinus of the dorsal surface, 

 but not quite as wide, and open nearly to the dorsal surface, except 

 where it is crossed by a protuberance from the ventral portion of the 

 ophthalmic lobe (c, figure 2). 



On the upper surface of the carapax, the orbital sinus, each side, is 

 completely filled by the dorsal part of the ophthalmic lobe, of which the 

 anterior margin is slightly concave in outline and continuous with the 

 anterior margin of the carapax, but has a small tubercle near the mid- 

 dle. The dorsal surface of the lobe is smooth, calcareous and opaque, 



