Hambach — Revision of the Blastoideae. 11 



think has not been done so far. But in the case under con- 

 sideration, that is in Pentremites and allied forms, the body 

 is dicyclical, which it could not be if the deltoids were inter- 

 radial. In that case the apex of the deltoid, i. e., the lateral 

 expansion, would be the base and not the apex and hence 

 would have been developed first, which is not the case as I have 

 shown above, — Plate VI., Fig. 1-3. However large or small 

 the lateral expansion of the deltoid may be, the fact is that 

 the base part of the deltoid is developed first and is the prin- 

 cipal part of the body. It is not separated from the laterally 

 expanded part by any suture. All principal openings are 

 constructed by this part, or together with the lancet piece, or 

 the openings pierce the deltoid piece. They do not rest upon 

 the upper sloping sides of the fork pieces or radials but the 

 fork pieces lean against the deltoid piece whether the laterally 

 expanded part is developed or not. Therefore it is hardly 

 possible to assume that such important pieces as the deltoids 

 should have been developed later than less important ones, 

 which is sufficiently demonstrated by the foregoing pages. 

 For these reasons they cannot be interradials. 



LANCET PIECES. 



The lancet piece varies very much according to the dimen- 

 sions of the fork piece sinus, ^. e., according to the species, 

 from a regular lancet-shaped piece to a mere linear lamella and 

 fits in the sinus of the fork piece in such a way as to fill the 

 incision with the exception of a narrow fissure on each side. 

 They are in the typical forms, as Pentremites sulcatus, P. 

 JlorealiSy P. pyriformis, etc., as substantial as the other parts 

 of the calyx and form an integral part of the calyx of the same 

 value as the other pieces constructing it, and are in large 

 specimens of P. sulcatiis fully one eighth inch thick. They 

 are generally of uniform width with a smooth anterior surface, 

 whereas the posterior or inner surface is more or less concave 

 and has a semi-lunar groove throughout its length for the 

 reception of some duct or vessel. On the upper or base 

 portion is a little beak-like process of a triangular form 



