416 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



either side, between the brancliial region and the posterior part of the 

 gastric and the cardiac region, and with the surface rough and tuber- 

 culose. The cardiac, with the posterior part of the gastric region, is 

 raised into a continuous ridge, capped with a longitudinal line of four 

 large spiniforin tubercles, one on the gastric and three on the cardiac, 

 besides a small one in the middle of the posterior margin. The cardiac 

 and the two anterior gastric tubercles are erect and their tips nearly in 

 the same horizontal line, while the posterior cardiac is situated much 

 lower down on the posterior slope of the carapax and is directed upward 

 and backward. In front of the gastric tubercle there are two much 

 smaller ones, in a transverse line, and in front of these there are usually 

 four still smaller ones similarly disposed, so as to make a submedian 

 line of three small tubercles either side, between the large gastric tubercle 

 and the erect and promment tubercle upon the crest of the orbital arch. 

 In one of the specimens the most anterior of these three pairs of tubercles 

 back of tbe orbits is obsolete. There is a deep longitudinal depression 

 between the orbits, and extending a little back of them and forward to 

 the narrow i^art of the rostrum. The rostrum is prominent, directed 

 forward and downward, suddenly contracted just in front of the antennal 

 fossae, leaving a dentiform tubercle either side, where the rostrum is 

 suddenly narrowed ; there is also a small tooth either side, near the tip 

 of the rostrum. The anterolateral margin is strongly incurved at 

 the cervical suture, so as to approach closely and expose slightly from 

 above the strongly tuberculo-dentate, infero-lateral carina, which is itself 

 slightly incurved at this point ; both in front of and behind the cervical 

 suture, however, the margin recedes from the inferior carina, in front 

 being directed upward at an oblique angle with the part behind the 

 cervical suture. Above this angle there is a broad, conspicuous, and 

 nearly smooth depression in the nearly vertical surface. The margin 

 between the cervical suture and the orbit is armed with two small tuber- 

 cles near the cervical suture, but the anterior two-thirds is unarmed and 

 slightly concave in outline. Behind the cervical suture the margin is 

 regularly and very strongly arcuate, and in front of the great branchial 

 tooth, which really forms the lateral angle of the carapax, is armed with 

 nine or ten teeth, of which the first three or four are small and some- 

 what tuberculiform ; the six jiosterior are larger, acutely triangular, and 

 strongly laciniated, the four anterior of these six being nearly equal in 

 size, the fifth larger and the sixth smaller than the others. The greatest 

 breadth of the carapax is between the tips of the large fifth laciniated 

 tootb each side, or, excluding the teeth, between the bases of the third 

 and fourth teeth each side. The great branchial tooth is larger than 

 any other, laciniated, and has a small tooth at the base in front and a 

 larger one near the base behind ; and still behind this last there is first 

 a small and then a much larger tuberculiform spine on the concave 

 postero-later.d margin, while the short posterior margin is armed with 

 three prominent tubercles, with several smaller ones between. The 



