86 THE TEETIAKY FOSSIL ECHINOIDEA 



In T. costatus the interradia closely resemble those of T. tuherculosus. The true 

 shape of T. costatus is high, that of T. tuherculosus is broader and more depressed, and 

 that of T. ajffmis, nobis, is still more depressed. 



4. Temnbchinds affinis, Duncan & Sladen. Plate XIII, Figs. 11, 12. 



The test is turban-shaped, broader than high, rather flat actinally, tumid at the am- 

 bitus, and less so in the more conical upper part, and depressed abactinally. Test symme- 

 trical ; peristome very small, and cuts small. Apical system small. At the ambitus the 

 width of an ambulacrum is very nearly equal to that of an interradium. Poriferous zone 

 broad, slightly sunken : pairs of pores in triplets, but in simple succession ; each pair is 

 placed on the lovper slope of a narrow costulate process ; the upper pair of each triplet has 

 its costulate process continuous with the ambulacral plate, on which is a small tubercle, 

 and the other two are in relation with the small primary tubercle, which is on the two 

 lower plates in the interporiferous area. There is a vertical row of small primary 

 tubercles on each side of the interporiferous area near the poriferous zone. Each of 

 these small primaries is connected with the smaller tubercle above the primary in the 

 lower plate by a narrow process. Eib-like processes cross the interporiferous space 

 from the small primaries and smaller tubercles of one vertical series to the other ; their 

 direction is oblique and in zigzag, and they are narrow from above downwards, granular 

 or minutely tuberculated, and usually the largest of their tubercles is near the primary 

 whence they originate. This raised ribbing produces broad and rather low (that is, 

 vertically) fossettes, and their shape is that of a broad straight comma. There is a 

 vertical row of these fossettes on either side of the median line of the ambulacrum. In 

 the interambulacra there are two vertical rows of small primaries, which are slightly 

 larger than those of the ambulacra; they are nearer the poriferous zone than the 

 median line, are wide apart at the ambulacrum, and the raised surface on which each 

 tubercle of a series rests is connected with that of the tubercle above and below by a 

 constricted process. 



Long and rather narrow zigzag ribs pass from near the primaries across the median 

 line to those of the adjoining plates, and smaller costse join on to those of the poriferous 

 zone on the other side of the primary tubercle. Small vertical costulate processes pass 

 from the actinal edge of one zigzag to the abactinal edge of the one below, and thus 

 interfere with the continuity of the very long transverse fossettes. Usually there are 

 two of these processes in each fossette between the two rows of primaries, and there is 

 one on the other side of the primary and between it and the poriferous zone in a 

 well-marked fossette there. So that, including the large vertical processes between the 

 tubercles of each vertical series, there are eight vertical raised lines, more or less costulate 

 and ornamented, in each interradium. Nearer the abactinal surface the breadth of the 

 fossettes diminishes, and one of the smaller vertical series is not seen ; and quite close 

 to the apex there is only the main vertical series of each side, which connects the 

 primaries above with the one placed actinally to it. The result of the presence of 



