588 TRIPYLUS. 



actinal side the tuberculation of the anterior part of the test is coarse, 

 distant, decreasing rapidly in size towards the ambitus, and remaining toler- 

 ably uniform over the actinal surface, diminishing in size somewhat towards 

 the apical system ; larger tubercles are found on the edges of the sunken 

 ambulacra, and on each side of the anterior groove. The spines are short, 

 club-shaped, slightly curved, grooved at the tip, and somewhat flattened; 

 they vary in length according to the size of the tubercles, but, apparently, 

 not materially in shape. 



Philippi, in his description of this species, mentions finding in each one of 

 the posterior ambulacra a small sea-urchin, which he takes to be the young 

 of it. It is totally unlike the adult, and seems to be a stage previous to the 

 development of the petals. When the mode of development of this species 

 is better known it may throw some light upon the apparently abnormal 

 mode of development, discovered more recently by Grube, in a species of 

 (Echinobrissus) Anochanus. Color of dried specimens is yellowish-brown 

 test, with greenish-gray spines. 



I could find no trace of the subanal fasciole in the specimens I have ex- 

 amined, such as has been figured by Philippi ; he does not mention it in the 

 text of his description. 



(HEMIASTER) Tripylus. 



Tripylus l'mi.., 1845, Wir_' Aivhiv. 



Test depressed, heart-shaped ; apical system anterior. Lateral ambulacra 

 sunken ; anterior groove slight: Actinal side flat. Peripetalous fasciole, 

 with continuous lateral and anal fascioles. This subgenus represents the 

 Schizaster type of Hemiaster. 



Tripylus excavatus 



! Tripylus excavatus Phil., 1845. Wieg. Arcliiv., p. 344. 



pi xxr.f. 4. 



Test thin, depressed ; outline from above heart-shaped, slightly truncated 

 posteriorly ; apical system slightly anterior to centre ; vertex posterior, half- 



