2() 8VEN LOVEN, ECHINOLOGICA. 



tliat tlie reabsorptiou is continued at a gradually reduced rate, 

 and in the adult probably attains a minimum. 



The buecal membrane devoid of pedicels is of all but uni- 

 versal occurrenee among the Ectobranchiata wlien adult, and 

 almost eharacteristical of their group. One family alone makes 

 an exception, that of the Echinothurida*. These exhibit a strue- 

 ture of the buceal membrane comparable in a certain degree 

 to that whieh characterizes the Cidarida?. I venture to take 

 the Asthenosoma varium of Grube as an example. FJ. XI L 

 fig. 161, gives the outside view of the peristomal region, dravvn 

 from a photograph. The woodcut p. 27 fig. 1 represents the 

 peristome seen from the inside, the auricles being omitted, 

 while fig. 2 — () give the same parts of the five ambulacra seen 

 from the outside, the plates marked with corresponding numbers. 



In this genus the ambulacra are much broader in propor- 

 tion than in the Diadematidffi, at the ambitus half as broad 

 as the interradia, and gradually contract, not expand, towards 

 the peristome. liaving there about 0,8 the breadtli of tlie 

 latter. Their plates are compound, numerous, and low. They 

 are triads consisting of one entire, aboral, plate and two 

 adoral demi-plates. The entire plates are imbricated down- 

 waid. adorallv, bv means of an inner rounded lameliar lobe, 

 shaded in the woodcut fig. 2 — 5, emitted aborally near the 

 mesial, sutural end, and overlapped by the following plate; 

 laterally they have shorter lobes overlapped by the interra- 

 dium. The demi-plates are minute, contiguous, received into 

 an emargination of the entire plate; near the calyx and ven- 

 trally they are broad. somewhat rhomboidal, and placed dia- 

 gonally, towards the peristome more triangulär; dorsally on 

 the flanks laneeolate, and placed almost in a transverse line. 

 the middle one rather elongated, the inner one submesial. They 

 have, there, no lameilar lobes or very slight ones. The pores 

 are disposed into ascending rows of three, arched on the 

 ventral side, nearly straight and transverse dorsallj-. The 

 outer pore in every row, the first one from below, is that of 

 the entire plate; the other two belong to the demi-plates of 

 the next triad. If the plates of any such row of three pores 

 are numbered 1. 2. o, the 1 being the entire plate, the 2 and 

 o the demi-plates of the preceding compound plate, the fixed 

 ambulacral columns I a, II a, III b, IV «, V b, are found. 

 in the specimen figured, to terminate at the peristome with 



