84 DAVENPORT ACADKMV OF NATURAL SCTENCKS. 



Heteroschisma gracile Wachsmuth, Nov. Sp. 



Heteroschisma gracile Wachsmutii. 



Fig. /, side view of ;i specimen. Fig. 2, horizontal section of the hydrospires. The first 

 fig^ure enlarged three diameters, the otlier five. 



Body subclavate or irregularly pyriform, pointed at the base, deeply 

 excavated in the direction of the rays. From the foot of the basals to 

 the radial sinus the form is elongate-obconical, the sides straight, 

 or nearly so. The radials are arched, with an angularity along the 

 median line, which culminates in the lips, but almost disappears on 



Cadaster altenuttus (Owen's (Jeol. Rej)., \'ol. III., p. 493), evidently took all I^ouisville Blas- 

 toids containing hydrospire slits to belong to only one species, and this makes it difficult to 

 ascertain now to which of the forms the name should be applied. His generic figure, on PI. V., 

 P^'n- .3> represents, undoubtedly, the form which afterwards was described by Shumard as 

 Cadaster pyrcnnidatiis (Acad. Sci., St. Louis, V^ol. I., No. 2). Lyon's Fig. 3 h gives a small 

 specimen of the same species; his Fig. 3 n, however, is not only an entirely different species, but 

 a Heteroschisma. It might appear that the form represented by the first figure .should receive 

 Lyon's name, but this would do injustice to Shumard, the more as Lyon's descriptions are fitted 

 for neither the one form nor the other. It must be further considered that the latter form, 

 which, like Heteroschisma gracile, has small interradials and large pyramids formed by the 

 limbs, is readily separated again into two sections, the one larger, more elongate, and decidedly 

 clavate, with nearly sti-aight sides ; the other smaller, with convex sides, and somewhat larger 

 and more prominent interrudial plates, lender these circumstances, I would be probably justified 

 to drop Lyon's name entirely, but, not wishing to overburden the literature unnecessarily with 

 names, I propose to apply his specific name to the smaller form, as this is probably represented 

 by Fig. 3 a, and which will be known as Heteroschisma alternatum. The larger type, which 

 possibly may represent a more adult form of the other, but more jirobably is a good variety, or 

 even an entirely distinct species, can be distinguished as Heteroschisma alternatum, var. elon- 

 gatvm, which may be changed into //. elongattim, should the above characters be considered 

 sufficient for specific distinction. Shumard's species is easily recognized by being much more 

 flat-topi)ed, that it has large interradials, and these abutting against the deflected upper ends of 

 the limbs, and that the radials generally possess along the lateral sutures, near the margin, one 

 or more rather dee]i, longitudinal grooves. Lyon, in asserting that the hydrospiral grooves 

 were " probal)ly capable of being compressed or impressed," made the mistake of taking speci- 

 mens of Cadaster pyramidatits as the compressed, and those of Heteroschisma alternatum .as 

 the impressed, condition of his species. It should be further remarked that none of the Louis- 

 ville specimc-ns, upon which Lyon based his dicyclic base in Cadaster, show any such structure. 



