48 G. P. MATTHEAV ON THE 



species the cardinal area is sliori and the beak quite low, and as the convexity of the two 

 valves does not differ greatly, this appears to be the form which Wahleuberg had iu view 

 when describing the species. Dalmau's description, on the other hand, applies best to a 

 variety [alrypoiaea) described and figured by the writer in the sequel. He, like Wahleu- 

 berg, appears to describe only the ventral valve. 



Leopold vou Buch, while recognizing the distinctness of the two valves, ascribes a 

 sulcus to the ventral valve, which apparently has not been observed by any other writer. 

 With tais exception, his description applies to the type of the species ; that is, the evenly 

 lenticular form with a short hinge line. The extreme thinness of the shell fully bears 

 out Dalman's remarks on this point, and is associated with inconspicuous hinge teeth and 

 dental plates. The internal markings of the shell produced by attachment of the muscles 

 and the ovarian spaces are only faintly indicated and often quite indiscernible. 



Sculpture. — There is a wide variation in this respect in examples of different ages and 

 in the different varieties. As a rule the young shells, especially those of the ventral 

 valve, are smooth, with only slightly marked diverging ridges. In the Acadian examples 

 of this species the sculpturing is always more distinct on the dorsal than on the ventral 

 valve ; this I find also is the case with the Swedish examples, for which I am indebted to 

 Dr. Lindstrom. 



As the shells grew larger the ribs became more distinct and also more numerous by 

 the intercalation of new ribs towards the margin. Leopold von Buch giA'es 18 to 20 as 

 the full number of ribs in the adult. This is the usual number iu the St. John examjjles, 

 though a few show as many as 30. 



Size. — The largest example of this species observed at St. John is 8 mm. long and 11 

 mm. broad, but Brogger mentions that an example from Toien, Vestfossen, was 10'5 x 12'5. 

 Dr. Lindstrom has not seen any so large. A medium size of shell, about 5x6 mm., is by 

 far the most common in the Acadian rocks. 



Horizon and Locality. — This species is found in limestone lentiles, enclosed in the 

 black shales of Division 3 a, at Germaine street, St. John, occurring together, as iu Sweden, 

 in great numbers and of all sizes. 



VARIETIES. 



Associated with the typical form of this shell are a number of allied forms, which 

 might at first be thought to be distinct species, but which by intermediate forms, and 

 especially in the young shells, seem to run together. Dalman says that in Sweden " no 

 other form of Terebratulite is found with this species," and as the forms found in Acadia 

 are perhaps but varieties of one species, they are_thus described here. 



Var. atrypoides. (PI. XII, figs. 11 « and b.) 



This form is comparatively smooth, though the ventral valve is sometimes concen- 

 trically wrinkled. This valve is distinguished by a median ridge and somewhat flat- 

 tened sides, and the dorsal valve has an unusually deep sinus. Size of the known 

 examples 6x6 mm., and 5x6 mm. for the two valves. 



