THE CRETACEOUS PERIOD. 187 



support to the first of the above suggestions, since the sea-urchins 

 have considerable range in depth, and forms not unlike those of the 

 Cretaceous are now dredged from deep water. 



In the clastic formations, the pelecypods and gastropods furnished 

 a notable and characteristic element (Fig. 417, j-p). It will be seen 

 by a glance at the figures that they were making progress in moderni- 

 zation. The cephalopods were still a dominant feature, though the 

 ammonites were in their decline, and were showing erratic divergen- 

 cies of form attended by much ornamentation similar to that which 

 marked corresponding stages of the trilobites and crinoids. Odd 

 forms of partial uncoiling, or of spiral and other unusual forms of coil- 

 ing, were striking features. Fig. 417, e and h, illustrate two of these. 

 The aberrations were not usually systematic, but affected various 

 genera and species, and even the same individuals differently at different 

 stages, some being quite symmetrical up to a certain age, and then 

 becoming erratic; but even this does not hold universally. It lends 

 some little plausibility, however, to the view that these eccentricities 

 mark the senility of the race. An interesting form perhaps to be 

 classed here was the Baculites, which resumed the straight form of 

 the primitive Orthoceras, while it retained the very complicated suture 

 of the Ammonites (Fig. 417, g). Typical forms of the ammonoicls are 

 shown in Fig. 417, b, c, d, and these are to be regarded as repre- 

 senting the main lines of progress. The belemnites were abundant, 

 represented particularly by Belemnites and Belemnitella. These also 

 were nearing the end of their race. 



Special faunas. — On the Atlantic coast there were, at the north, a series of 

 subfaunas corresponding to the Ripley fauna at the south, and above these 

 (New Jersey and Maryland), there were faunas not found at the south. 1 

 The earliest faunal group at the north embraced the sub-faunas of the 

 Mer chant ville, Woodbury, Marshalltown, and Wenonah beds, and corre- 

 sponded essentially with the fauna of the Matawan formation. 2 In the Mer- 

 chantville sub-fauna, Axinca mortoni, Idoncarca antrosa, Trigonia eufaulensis- 

 and Panopea decisa are abundant. In the Woodbury beds next above, most of 

 these are rare, and Cyprimcria, Breviarca, Lucitia cretacea, Cancellaria subalta, 

 and others, rare or absent below, become the commonest species. In the Marshall 

 town beds, Trigonia, Cyprimcria and Idonearca vulgaris are abundant, while 



1 See Reports of Maryland and New Jersey. 



2 Weller and Knapp, The Classification of the Upper Cretaceous Formations and 

 Faunas of New Jersey, Jour. Geol. XIII, 1905, pp. 71-84. 



