MONOPHORA DARWINII. 13 



is intermediate between it and Encope proper, though in such forms as En- 

 cope Michehni and Encope grandis it is difficult to trace the precise Hmits 

 of these subgenera. 



Monophora DarTvinii 



Monophora Darwinii Desor, 1847, Bull. Soc. Gdol. Fr., IV. p. 287. 



PI. III. f. 1-3. 



At first glance, seen from above, this species would be taken for an Echina- 

 rachnius, wnth a posterior interambulacral lunule ; the actiual anibulacral 

 cuts are reduced to slight angular indentations, giving the nearly circular 

 outline of the test a lobed appearance. The apical system is somewhat ec- 

 centric posteriorly ; the ambulacral petals short, extending but little beyond 

 half-way to the edge of the test from the apex. The odd anterior petal is 

 somewhat longer than the anterior pair ; they, in their turn, are longer than 

 the posterior ones. The poriferous zones are broader than the median inter- 

 poriferous space ; the poriferous furrows distinct and closely crowded with 

 pores. The vertical margin of the test is covered by two or three irregular 

 rows of large tubercles, larger than any on the actinal surface. The edge 

 of the lunule is raised on the abactinal side, where it is small, elliptical ; 

 on the actinal side it is larger, and connected by a shallow groove with the 

 anal opening ; the latter is placed about half-way between the edge of the 

 test and the actinostome. The actinostome is, like the apical system, ec- 

 centric, posteriorly circular, with prominent buccal tubes. 



San Mathias Bay (probably tertiary). 



PALEOPNEUSTES. 



Paleopneustes A. Ac, 1873, Bull. M. C. Z., m. No. 8, p. 188. 



One of the most interesting of the Spatangoid genera dredged by the 

 Coast Survey Expeditions is undoubtedly Paleopneustes, the representative in 

 our days of Ananchytes, one of the most prominent and most common creta- 

 ceous genera, and resembling it in outline and general appearance to such an 

 extent, that the only species of this genus thus far obtained would, at first 

 sight, readily pass for Ananchytes gibbosa. A closer examination of the 

 denuded test shows that, unlike Ananchytes, the upper part of the lateral 

 ambulacra is imperfectly petaloid. The abactinal system is like that of true 

 Spatangoids, generally compact, and not elongate, — a structural feature which 



