HAMBACH ANATOMY OF THE GENUS PENTREMITES, ETC. I47 



was composed of twice three pieces ; but numerous examinations 

 of isolated pelves have convinced me of the fact that this furrow 

 is only superficial and not a separating suture. It is correctly 

 described b}' Quenstedt.* 



The Forked pieces. — The foi-ked or radial pieces are five in 

 number. In shape they resemble a rectangle in which the upper 

 corners are wanting. The forked appearance is due to a sinus, 

 of varying depth, which runs obliquely from the superior margin 

 inwardly, so that the surface between its external margins is 

 larger than that between the internal ones. It slopes towards 

 one side and thus gives each prong a more or less three-cornered 

 appearance. The internal oblique surfaces of the prongs are cov- 

 ered with a number of minute transverse ledges (Plate a^ Fig. 2) 

 which connect them with the poral pieces. At the base of the 

 sinus are two little crests to support the apex of the lancet pieces. 

 The base of the fork pieces, as indicated by the sinus, varies very 

 much in form and size from a little lamella barely large enough 

 to furnish a support for the prongs, to a most solid and substan- 

 tial part of the piece : see Plate a. Fig. 20:, as in P. sulcatus and 

 others. In such cases the transverse diameter of the fork pieces 

 at the apex of the ambulacral field presents a triangular or semi- 

 lunar form with the greatest surface at the point from which the 

 external surface slopes downward and inward : see Plate «, Fig. 

 3. The lower margin forming the connection is then equally as 

 thick as that of the basal pieces. The interior surface of the base 

 portion of such a fork piece, which in some cases is as large or 

 larger than the prongs themselves, is straight or concave, and the 

 form of cast accordingly receives such modifications that it may 

 seem to belong to an entirely different individual ; for example, 

 Pentremites later?z(for7}iis (Shum.) is a cast of P. sulcatus. ■\ 



* Quenstedt, Handbuch der Petrefaktenkunde, p. 755. 



t It seems that it is not generally understood to what species the cast described by Dr. 

 Shumard as Pentremites laterniformis belongs ; for S. A. Miller, as well as the Doctor, but 

 not Rcemer, takes it to be identical with P. ohliqtiatus (see Miller's Palaeozoic Fossils, p. 

 £6, and Trans, of the St. J.ouis Acad, of Science, vol. ii. p. 3S4) . I will state here that I 

 have seen the original specimen serving the Doctor for his description and that I afterwards 

 collected specimens in the same locality from which the Doctor's specimen was obtained, 

 showing P. sulcatus (Rcemer) on one side and the laterniformis on the other side see 

 PI. B, Fig. 10), convincing me without doubt to which fossil this cast belongs. The lower 

 pentagonal portion of the body is due to the straight inner surface of the lower part of the 

 fork pieces. 



