Prof. P. Martin Duncan — On Galerites alhogalerus, Lamk. 17 



median line of the ambulacrum. These plates are in sets of three : 

 the upper one is low and long and rectangular ; the next is trian- 

 gular with a curved outer edge close to the pores, and the third is 

 irregular in shape, being taller at the median line and of the same 

 height as the other two at the poriferous side. The pairs of pores 

 are not near the sutures of the ambulacral plates ; and above the 

 margin of the test the direction of the two pores is oblique : one pore 

 being above the other and towards the inter-ambulacrum. But 

 below the margiu the upper pore gets first directly above the other, 

 and then obliquely, being above and towards the median line of the 

 ambulacrum. This obliquity is increased where the triplets occur. 



Each triplet comprises a set of three ambulacral plates as described 

 above. The pair of pores (of the triplet) nearest the ambulacral median 

 line is on the upper rectangular plate ; the next pair a little further 

 out towards the interambulacral edge of the ambulacral plate is on 

 the triangular plate, and the third pair further out still, is on the 

 lowest and largest plate and close to its interambulacral edge. The 

 two ambulacral plates closest to the peristome have according to the 

 ambulacrum one pair on one side of the median line and two on the 

 other side. The arrangement of the triplet is unlike that of any 

 other genus. 



There is a point of considerable importance about the peristome, 

 its edge is carried upwards very slightly in the interambulacral 

 part so as to produce the rudiments of a tube, which is very evident 

 in such genera as Amhlypygus for instance. 



The position of Galerites alhogalerus =. Echinoconus conicus as a 

 toothed form can no longer be maintained. It has a singularly con- 

 centrated apical system and but four genital plates. The ambulacra 

 reaching from the ocular plates to the peristome and widening out at 

 the margin of the test have intercalated small triangular plates, and 

 the direction of the pores of the pairs alters. The triplet arrange- 

 ment has nothing to do with extra plates, and is produced by the 

 position of the penetration of the successive plates by the tentacles. 

 Five pair of buccal plates exist in well-preserved specimens. 



With regard to the construction of the base of the test, it may be 

 observed that there are 6 plates between the peristome and the peri- 

 proct, and that the 7th from the mouth enters into the composition of 

 the periproct, as also do the 8th, 9th, and 10th. 



Un the whole, the test is thin, and there is a specimen in the 

 British Museum which shows that an inward bulge was produced 

 during life. 



The genus Galerites, and possibly some others which have hitherto 

 been associated together in the family Galeridee, must join some 

 atelostomatous group. Lately Mr. Percy Sladen and myself^ have 

 shown the affinities of the genus Amhlypygus and Echinoneus, and it is 

 evident that only the oblique mouth and certain peristomial plates 

 separate these genera from Galerites. It should stand amongst the 

 Echinonida3, a sub-family of the Cassidulidge, of the sub-order Atelo- 



^ Fossil Ecliinoidea of Kachh and Kattywar, Pal. Indica, ser. xiv. vol. i. part 4, 

 1883. 



DECADE III. VOL. I. NO. I. 2 



