1889.] NATURAL SCIENCES OF PHILADELPHIA. 287 



the deposition of the Kinderhook and Burlington beds. When the 

 strata of the first were being laid down it would seem that in the 



vicinity of the present city of Burlington there was very shallow 

 water, which probably did not have, at all times, free connection 

 with the open sea. But in the succeeding epoch it is evident that 

 the depth of the oceanic expanse considerably increased at that 

 place. 



In the Kinderhook there is a notable absence of certain classes of 

 animal remains, principally crustaceans, echinoderms, corals, and 

 bryozoans; while in the Burlington these groups, excepting perhaps 

 the articulates, are well represented. On the other hand the mollusca 

 were particularly abundant in the lower, but of rare occurrence in 

 the upper, division. Bryozoa are rare ; brachiopoda abundant. The 

 cephalopoda are represented by several genera, but individually they 

 are not common ; none have been as yet observed in the superim- 

 posing layers. Of the pteropoda several species of Conularia have 

 been obtained. The lamellibranchiata are quite plentiful and with 

 the exception of two genera are not found in the limestones above. 

 The gasteropods include upwards of fifteen genera and fifty species. 

 But only two of the generic groups — Platyceras and Straparollus — 

 have thus far been recognized in the Burlington strata, in which 

 there occur eight species of the first genus and two of the second. 

 In the Upper Burlington Platyceras is especially common and 

 is often found attached to the ventral surfaces of crinoids. It i> 

 worthv of note that several of those shells observed adhering: to the 

 stalked echinoderms are specifically identical with certain Keokuk 

 Platycerata and that in both horizons the various forms of gasteropods 

 are associated with crinoids of similar anatomical construction. 

 Some of the species of Platyceras which are first known in the upper 

 Burlington became in the Keokuk very abundant, and widely 

 distributed geographically. It may also be remarked that the 

 Keokuk forms seem to follow the Burlington species in direct 

 biologic sequence ; but that between the Kinderhook and Burling- 

 ton no such close affinities are traceable in this genus. 



The Straparolli of the Burlington rocks are all angulated forms. 

 In .S'. lotus Hall there are two well defined angularities — one on the 

 upper side of the whorls ; the other on the under side. The 

 latter is usually more or less rounded ; but the former is generally 

 surmounted by a narrow carina which gives it additional prom- 

 inence. The upper surface of the volutions is flattened and the 



