96 BRITISH PALEOZOIC ASTEROZOA. 



oF the series. The tube-feet in this portion of the arm were in consequence 

 arranged in quadriserial rows. It is also noteworthy that the ambulacralia are 

 high and thin. 



From the fifteenth ambulacral onwards the tube-feet become biserial in 

 arrangement, and the ambulacralia squarer in outline. The primitive appearance 

 of the ambulacralia and adambulacralia in the more distal region of the arm is 

 shown in Text-fig. 54 a. (See also p. 20 of the Introductory Section to this 

 Monograph.) Pores for the passage of ampullse are present between some of the 

 ambulacralia of the proximal portion of the arm, and may be seen as small v-shaped 

 slits on PI. IV, fig. 3, at the upper extremity of the figure near the axillary 

 interbrachial. 



55 



56 



Text-fig. 55 (on left).— Eeconstruction in plan of mouth-region of Promopitlaasfer elizcf (based on 



D. 51). X 9. 



Text-fig. 56 (on right). — Wash drawing of the proximal region of the ambulacral groove of 



PromopalfBaster elizcB (based on D. 51). x 12. 



There are twelve adambulacralia to the first nine infero-marginalia. From that 

 point tlie adambulacralia become equal in number and alternate in arrangement 

 with the infero-marginalia. There are twenty-four infero-marginalia in the longest 

 portion of an arm preserved. 



Interior View. — D. 119 and D. 2-57 are both interesting as they show the form 

 with the apical covering plates removed, so that one can look down into the body- 

 cavity in the mouth-region. Both specimens show an unmistakeable yshaped 

 odontophor in each of the interradial angles. Although one cannot be certain, I 

 am almost convinced that this odontophor is merely the dorsal prolongation of the 

 plate called by Schuchert the " axillary interbrachial." This view is supported 

 by the observations made on Girvanaster scidptus (see p. 72). 



D. 257 is also interesting as it shows a cast of a Gasteropod shell inside the 

 mouth-cavity. Even these older Asteroidea had their molluscan diet. 



Description of D. 26 and D. 26c (Text-figs. 57 and 58). — At first sight casts 

 from these imprints appear to belong to a distinct species, but the arrangement of 

 the mouth-parts and the oral interradial areas is, so far as can be made out, that 

 of the type. I am inclined therefore to regard the specimen either as a growth- 



