MOLLUSCA. 673 



1861. Scala Sillmani Gabb, Synop. Moll. Cret, Form., p. 135 



(79). 

 1864. Scala Sillmani Meek, Check List Inv. Poss. N. A., Cret. 



and Jur., p. 20. 

 .1892. Scalaria Sillmani Whitf., Pal. N. J., vol. 2 (Monog. U. S. 



G. S., vol. 18), p. 138, pi. 18, fig. 2. 

 .1905. Scala sillmani Johns., Proc. Acad. Nat. Sci. Phil. (1905), 



p. 20. 



Description. — "Shell of medium size, measuring nearly one 

 inch in length and rapidly tapering, the apical angle being about 

 ,30° or 35°; volutions five or more, very round and full, but 

 closely compacted; the suture line deep and sharpi, but close; 

 aperture (as shown on the only specimen in hand, which is a 

 matrix containing the shell of one side of the specimen in place 

 and from' which a gutta-percha cast is taken for description and 

 -figure), is round, but the margin is not preserved; surface of the 

 shell marked by oblique varices, which have a slightly backwara 

 •direction in crossing from the upper to the lower side of the volu- 

 tion ; the varices are thin and recurved, and number eight on one- 

 half of the circumference of the last volution, but decrease some- 

 what in number toward the apex of the spire; axis imperforate, 

 the base of the last volution bordered by a raised carina, below 

 which the varices do not appear to extend. So far as can be 

 ascertained from the specimen, I should judge that the varices 

 were slightly produced in the upper part to form subspines around 

 the base of the preceding volution. The minute surface character 

 ■of the shell can not be ascertained from the specimen in use, as 

 •only the inside of the substance is revealed, but Dr. Morton 

 describes it as marked by 'very minute spiral striae,' which one 

 would suppose would naturally be the case. Mr. Gabb also 

 speaks of it having 'much finer' revolving striae than his Scala 

 (Opalia) Thom>asi, which is also a New Jersey species, and says 

 that 'each rib is reflected back into a little lip or notch at the 

 angle of the basal varina.' " (Whitfield.) 



The dimensions of a large specimen are: height, 31 mm. ; max- 

 imum diameter,- 18 mm. 



43 PAi. 



