the Morphology and Classification of the !Saleiuida3. 123 



proctal ring is usual in tliese species, and in some others, such 

 as Acrosalenia pustulata^ Forbes, in which the dorso-central 

 is accompanied by supplementary plates, the anterior radial 

 plate (III.) may enter the space between the antero-lateral 

 basals. All this persistence of a dorso-central, and its occa- 

 sional association with supplementary plates, and its growth 

 in relation to the other parts of the apical system, was accom- 

 panied by movement outwards of basal plates and inward 

 movement of radials. 



One of the later Acrosalenice [A. angularis) varies in the 

 nature of the plates accompanying the dorso-central, as may be 

 noticed in the figure given by Loven (' On Pourtalesia^ 1883, 

 p. 66, and de Loriol, Mem. Soc. Pal. Suisse, vol. xii. P"" supp. a 

 I'Echin. Helv. 1885, pi. i. fig. 4). This species is as interesting 

 as the last of the Acrosalenice. {^A. miranda, Cott., Peron, & 

 Gauth., Ech. Foss. de I'Alger., 2" part. p. 86). This Neoco- 

 mian species has the dorso-central large, central, and separated 

 from the periproct by some small periproctal plates. 



It appears that in Acrosalenia some species have a perfect 

 dorso-central with an angular posterior part ; others have it 

 eroded for the periproctal ring ; others have small supple- 

 mentary plates between it and the ring or elsewhere. 



There is a very important character which is present in all 

 the species of Acrosalenia ; it refers to the so-called cuts or 

 branchial grooves at the peristome. These grooves and inden- 

 tations of the peristome are very well developed and are 

 large for the size of the test; they pass up on the outside for 

 a short distance along the line of the interradio-ambulacral 

 sutures, and each one is bounded by a raised rim or edge. 

 Although Desor stated to the contrary, these grooves are well 

 seen in good specimens, and give a marked character to the 

 genus. The corresponding parts are small in the genus 

 Salenia, and it is now known that the branchi^ are small in 

 the recent species. It will be observed that in this character 

 Acrosalenia departs more from the type of the Cidaridse than 

 Salenia, and yet the first-named genus is the older one. 



The Perignathic Girdle. — Tiiis structure may be seen after 

 careful removal of the matrix when it is soft. The ridges 

 are broad and low, and the processes are moderately tall and 

 slender ; they do not usually arch over the ambulacra, buc they 

 may join at their free ends and thus arch in some sj)ecimens. 

 The type is not that of the Cidaridai, but of the other Endo- 

 cyclica (see Journ. Linn. Soc, Zool. vol. xix. p. 179). 



The Ambulacral Plates. — One of the reasons why the 

 Saleniidge have been considered to be closely allied to the 

 Cidaridae is that the ambulacral plates in both groups are 



