1872.] EXHEEIDGE NEW ECHraODEEM. 99 



broad ; base slightly concave. Dorsal and ventral surfaces densely 

 covered with equal-sized, apparently imperforate, tubercles*. An- 

 terior margin smooth, and slightly acute ; posterior margin broader 

 than anterior and possessing in the middle six tumid lobes or fimbria- 

 tions; three others, less tumid, occupy the right and left postero-lateral 

 margins (twelve in all). Ambulacra subpetaloid and equal. Apical 

 disk small, central, round, and covered by the madreporiform plate 

 and tubercle. Mouth central. Yent placed nearly halfway between 

 the mouth and posterior border, nearer the mouth. Tubercles of 

 one order. 



ROTTTIiOrDEA EIMBEIATA, Sp. UOV. 



Specific char. — Test thick, elongated, depressed ; upper and under 

 surfaces densely and equally covered with small, nearly equal-sized, 

 imperforate tubercles, all of which are surrounded by ring-like areolae. 

 Base slightly concave and covered by anastomosing, slightly im- 

 pressed, bifurcating avenues, meeting at the mouth ; these carry the 

 "interrupted" pores of the ambulacra. Ambulacra subpetaloid, 

 slightly narrowing on approaching the margin ; the right and left 

 postero-lateral pair sharply, or suddenly, diverge on leaving the apical 

 disk, and pass to the margin over two of the posterior crenulations, 

 ceasing to appear in pairs of "hole and sUt" about two-thirds down 

 the posterior area. The lateral pair of ambulacra do not diverge so 

 much as the postero-laterals, and occupy, with the odd ambulacrum, 

 the anterior half of the test. The odd or single ambulacrum is 

 straight, occupying the anterior margin. All traces of the pores in 

 the ambtdacra are apparently lost at the margin and base, save near 

 the mouth ; but on the ventral surface they are represented by five 

 slightly depressed, smooth-looking furrows, possessing numerous 

 small pores ; these furrows divide or ramify about halfway between 

 the mouth and margin. The inner row of pores in the poriferous zones 

 are small and round ; the outer slit-like, well-developed, and nearly 

 horizontal. Near the margin of the test the subpetaloid condition 

 of the ambulacra ceases, and the pores become unigeminal in single 

 file, a few in scattered pairs passing the margin over definite fimbri- 

 ations, after leaving which, all direct traces of them are lost amidst the 

 ramifying and anastomosing furrows at the base ; but they appear to 

 be trigeminal near the peristome. The posterior and lateral pairs of 

 ambulacra bear peculiar relation to the twelve crenulations occupying 

 the posterior half of the test : four lobes or fimbriations occupy the 

 space between the two extremities of the posterior ambulacra ; one 

 branch of each ambulaeral zone (consisting of a single pair of pores) 

 passes over the two lobes next the centre pair, thus occupying four 

 and enclosing two. On the lateral mai'gins two lobes occur between 

 the posterior and lateral ambulacra, which latter pass over (also in 

 single file) the two antero-lateral lobes, thus completing the twelve 



* In the living Botula Eumphii the puncta of the tubercles are so minute 

 as almost to defy detection microscopically ; it would be quite impossible that 

 they could escape destruction under fossilization and mineralization. The term 

 " imperforate," therefore, must be received with this reservation. 



