474 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



ambulacral areas. Beyond the third the brachials are united in 

 syzygial pairs as in GepJiyrocrinus, and the first two brachials are 

 similarly united. 



This new type may be known as 



THALASSOCRINUS, new genus. 



The characters of this genus are included in the description of the 

 type-species. 



Genotype. — Tlialassocrinus pontifer, new species. 



THALASSOCRINUS PONTIFER, new species. 



Stem. — The stem is 151 mm. in length and is composed of 169 

 columnars ; those immediately beneath the basals are discoidal, about 

 0.3 mm. in length and about 2.2 mm. in diameter, the diameter grad- 

 ually decreasing, after the proximal eight or ten being about 1.8 mm. ; 

 after the sixth traces of intercalated columnars may be found between 

 each two columnars, and after the fourteenth these intercalated 

 columnars entirely separate those on either side; after the twenty- 

 eighth there is no difference between the intercalated and the origi- 

 nal columnars; both have increased so that they are now 0.7 mm. 

 in height, remaining 1.7 mm. in diameter; at the fortieth they are 

 about 0.8 mm. in height with the same diameter, but now they 

 increase rather more rapidly in length, so that at the fif ty-tliird they 

 are 1.2 mm. long; after the proximal half of the stem they A^ery 

 gradually decrease in height, being distally about 0.8 mm. In the 

 last 50 mm. of the stem there is an almost imperceptible increase in 

 the diameter, which becomes rather more noticeable in the last 10 

 mm.; the diameter of the lowest columnar, the stem having been 

 broken off at or near the root, is 2.3 mm. 



At the top of the stem the columnars are hexagonal in outline, the 

 angles of the hexagon being occupied by rather prominent tubercles, 

 and these tubercles are practically alike on the succeeding columnars ; 

 after the eighth these tubercles become more prominent, for the reason 

 that the original columnars are separated by intercalated columnars 

 of lesser height, whose tubercles are only slightly developed; the 

 tubercles on the second, fourth, eighth, fifteenth, and twenty-third 

 columnars are slightly larger than those on the remainder; after the 

 twenty-seventh segment these tubercles somwehat abruptly become 

 much smaller and the columnars become nearly circular in outline, 

 each bearing about its middle six minute moderately sharp tubercles 

 which rise abruptly from the general surface; after the proximal 

 third of the stem these show a tendency to become obsolete on 

 alternate segments, and in the terminal third of the stem they have 

 entirely disappeared, so that the columnars are perfectly smooth; 

 after the proximal third of the stem the columnars appear to be 

 quite circular in outline. 



