94 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



outermost columns of each ray are regarded as the inframarginals 

 and the ones immediately inside as supramarginals, two medial 

 columns remain to be homologized with those in Mesopalseaster. If 

 Simonovitsch is correct, then by this interpretation there are two 

 columns between the supramarginals. Both can not be radials and to 

 regard one as such will leave a unilateral and apparently an unnatural 

 development. If five or seven columns of abactinal plates were present, 

 this species would be hi harmony with Mesopalxaster. Since Simono- 

 vitsch's work is of the best, we have at present the only alternative of 

 supposing that the radials in Asterias acuminatus are suppressed and 

 that its two medial columns are homologous with the intercalary 

 abactinal plates of other starfishes. Among Paleozoic asterids this 

 development is rare and is found only in Encrinaster and Palseaster. 

 In that event, A. acuminatus is not a Mesopalseaster. 



A single example of this species was found in the Lower Devonic 

 (probably Upper Coblenzian) near Braubach, Germany. 



In his revision of the Lower Devonic starfishes of Germany, 

 Schondorf was not able to discover the whereabouts of the type-speci- 

 men and therefore had to leave this species as determined by Simono- 

 vitsch. The former states that actinally the structure reminds one 

 of Spaniaster latiscutatus, the genotype of Spaniaster, and closely 

 related to Mesopalseaster. For further remarks see Spaniaster. 



MESOPAL^ASTER (?) CLARKI (Clarke and Swartz). 



Plate 10, figs. 1, 2. 



Pals&aster clarki CLARKE and SWARTZ, Maryland Geol. Surv., Upper Devonian, 

 1913, p. 543, pi. 46, figs. 3,4. 



Original description. "This species is represented in the collec- 

 tions by a single specimen affording a pretty sharp cast of both sides 

 of a very regular and complete individual. In general structure and 

 appearance the species is quite similar, especially on the oral surface, 

 to Palseaster eucharis Hall of the sandy Hamilton shales of central 

 New York, but the latter is a much larger form. 



"The disk is small, rays long and slender, thecal plates all promi- 

 nently developed. The ambulacral surfaces are represented only by 

 a narrow linear depression beneath which the ambulacral plates are 

 concealed. These depressions are bordered by thickened and somewhat 

 elevated quadrangular or pentangular ad ambulacra. The marginal 

 plates are in single rows, much thickened, with generally quadrangular 

 outline and convex surface, each projecting on the margin of the ray. 

 At each axilla is a single pear-shaped plate with its apex outward, 

 these plates being the largest in the individual. The abactinal surface 

 is tessellated by rows of strong convex plates of similar size to the mar- 

 ginal plates. Of these there are three rows, a median row of narrow 

 oval ones between the ends of which are interlocked the edges of the 

 much larger plates of the lateral rows which are highly convex and 



