NORTH AMERICAN LATER TERTIARY AND QUATERNARY BRYOZOA. 45 



This species is closely related to A. flemingi Busk. 1854, and A. trifolium Wood, both li^-ing in the 

 Beas of to-day and known also as fossils from late Tertian- beds of England and Italy. It is distinguished 

 from both by the lesser development of the frontal lamina. The constriction of the aperture ifl usually 

 more pronounced in A. constricta. 



„ . (?io = 0.30mm. ^ • (iz = 0.52-0.54 mm. 



Measurements.— Opesi&l^-^^ ^ ^ 22 mm. ^ooeciaj ^^^ q gg ^^_ 



Variations.— The cryptocyst is very little developed; it is more like a proximal 

 enlargement of the mural rim. By abrasion of the surface, the five dietellae are 

 easily visible. The beak of the avicularium is salient and rounded. The two 

 salient condyles arranged symmetrically in the opesium are intended to support the 

 articulation of the operculum. The ancestrula is orbicular, without spines. It 

 engenders one large and three small zooecia; the two groups are separated by two 

 large zooecia derived from the small ones. We have observed some calcified zooecia 

 perforated by a small median pore. Regenerated zooecia are rare. 



Affinities. — In a recent letter, Mr. Waters remarks that the differences between 

 this species and AmpUhlestrum flemxmji Busk, 1854, are not sufficient to separate 

 the two species. It is evident that we have here a difficult problem in specific deter- 

 mination and that we are not yet able to distinguish the true characters of the species 

 from those of a variety. The problem is further complicated by the great zooecial 

 variations. 



The micrometric measurements taken on the recent spechnens and on those 

 from the Helvetian of Touraine and the Tortonian of Eisenstadt, Hungary, are 

 always smaller than those of A. constrictum, a character which may be sufiicient to 

 maintain the American species. The American specimens also appear deprived of 

 oral spines. However, the specific name is a small matter if the illustrations are 

 good for careful comparisons. 



Occurrence.— Miocene (St. Mary's formation): Cove Point, Maryland (rare). 

 Miocene (Yorktown formation): 3 miles southwest of Petersburg, Virginia (rare). 

 Pliocene (Waccamaw marl): Waccamaw River, Horry County, South CaroUna 



(rare) . 



Plesiotypes.—Csit. Nos. 68456. 68459, U.S.N.M. 



AMPHIBLESTKUM TENXJIPARIETIS, new species. 



Plate 13, fig. 7. 



Description. — The zoarium incrusts shells. The zooecia are distinct, sepa- 

 rated by a deep furrow, hexagonal, rounded above; the mural rim is very thin, 

 rounded, very finely granulated; the cryptocyst is of httle depth, concave, gran- 

 ular; the opesium is oval, narrowed laterally by two condyles serving for articu- 

 lation of the opercular valve; it bears a concave or undulated proximal border. 

 The avicularium is elliptical, sahent, with pointed beak directed below. 

 ^ . fAo = 0.30mm. ^ • fZ2 = 0.55 mm. 



ifeasuremcnis.— Opesiaj ^^ ^ ^^^ ^^ Zooeciaj ^^^ q 45 ^^ 



Affinities.— The ancestrula is orbicular, garnished with very small spines, it 

 engenders three small and two large zooecia. 



This species is quite close to Amphiblestrum Jlemingi Busk, 1854; it differs 

 from it in the absence of gjTnnocyst, and in the larger ancestrular zooecia. It 



