316 Verrlll, JVotes on Radlata. 



In form and general appearance this species resembles Cassidulus 

 Carribcearum Lanik.,* of the West Indies. The positions of the 

 mouth and anal openings are nearly the same, and the latter is situated 

 in a similar transverse depression surmounted by an arched, lip-like 

 projection of nearly the same form, in each. 



The Cassidulus differs, however, in several structural features of 

 importance, — such as the number and arrangement of the poi-es in 

 the rosette around the mouth, and in not having the pairs of pores 

 in the dorsal rosette connected by transverse grooves, which, in P. 

 Pacifica, are deep and conspicuous and separated by rows of small 

 tubercles. 



BrisSUS obeSUS Ven-ill, sp. nov. 



Closely allied to B. colutnharis of the West Indies, and B. ScillcB, 

 Mediterranean, especially to tlie latter, from which it differs chiefly in 

 its proportions (as seen in profile) and the position of the vertex. 



The largest specimen is 2 inches long ; 1-55 broad ; 1-15 high, at the 

 most elevated point; 1"35 from abactinal center to posterior margin; 

 •92 to anterior margin ; 'OS to end of anterior-lateral ambulacra ; '80 

 to end of posterior ; "65 to end of anterior odd one (where crossed by 

 fasciole) ; sub-anal fasciole -75 broad, -25 long; "plastron" 1*20 long; 

 •70 broad at posterior end ; mouth ^40 broad. 



Viewed from above the form is regularly ovate, except the narrower, 

 posterior end, which is somewhat truncate and slightly emarginate 

 at the anal area. Distance from abactinal area to posterior end one 

 and a half times that to anterior end. The abactinal region is small 

 and scarcely depressed. The posterior interambulacrum is elevated 

 and swollen from its origin to the anal area, and subcarinated be- 

 tween the posterior ambulacra, caxising the latter to appear unusually 

 sunken. The region in front of the anterior lateral ambulacra is 

 regularly and pretty uniformly rounded, lacking the flattened, some- 

 what depressed anterior area seen in P. Scillce, and bears larger 

 tubercles than the rest of the test, as in the allied species. The ante- 

 rior odd ambulacrum is very narrow and scarcely depressed, with 

 rather indistinct pores. Those of anterior pair are moderately long, 

 lanceolate, nearly transverse, their ends curving somewhat toward 

 the anterior end. Posterior-lateral ambulacra longer than anterior 



* This species, which has recently been referred to Rhyncopygus by Dr. Liitken, was 

 the type of the genus Cassidulus when it was first established in the Systcme des 

 Animaux sans Vertebres, p. 348, 1801. Therefore it seems most proper to restrict the 

 genus Cassidulus to species like this. 



(This name is preoccupied in mollusca. Mr. A. Agassiz lias recently united this and 

 Pacificus in a new genus, Rhyncholampas, Bulletin M. C. Z., p. 270, — Reprint.) 



