Maryland Geological Sukvey '^'Jl 



volutions and four on the upper hall' of the external impression of tiie 

 body volution. The internal impression or mold of the body-whorl of 

 this same specimen shows at least six carinate ridges or spirals. Surface 

 marked by rather fine, closely arranged striae of growth. 



This description is based on the external and internal impressions of a 

 specimen which is intermediate between (7. liratuin Hall and C. multi- 

 liratinu Hall. It is probably nearer the former species and its most 

 marked difference is in tlie greater number of carinate; ridges on the liody- 

 whorl, since it probably has about eight while C. Viratum is given as having 

 about five, C. muUiliratum from ten to twelve, and C. hamiJtoniae from 

 fourteen to eighteen. There are some other rather slight differences in 

 these species ; ])ut the variation in the number of carinate lines is the most 

 conspicuous one. Dr. Grabau has clearly shown how these elevated lines 

 or " spirals " increase in number in the development of this general type 

 of Gastropoda. He says : " The primar}' ones are the first to appear, and 

 they increase in number by the exogenous appearance of new ones on the 

 upper and lower portions of the whorl, outside of those which appeared 

 first. Secondary spirals appear betiveen the primary ones as these diverge, 



owing to the uniform increase in size of the whorls This teaches ns 



that in the primitive type of a series we may expect to find primary 

 spirals only, even in the adult, and experience shows that these are char- 

 acteristic of the earlier memljers of any series." ' These specimens were 

 examined by Dr. Grabau who wrote as follows concerning the external 

 impression : " This is most interesting. It is a form between C. liratum 

 and C. hamiltoniae. It is nearer to C. liratum ; but has a secondary spiral 

 between the primary ones on the last volution. This indicates clearly a 

 more accelerated condition than liratum ; l)ut these have not yet become 

 so numeroiis as in hamiltoniae." Later he examined the internal mold 

 and stated that it "gives evidence of additional spirals. While this is 

 probably a descendant of the Ordovicic Cyclonemas it might be questioned 

 whether it had not better he placed in a distinct genus." The name of this 

 variety is given in honor of Dr. Grabau wlio first called my attention to 



' Amer. Nat., vol. xxxvi, Dec. 1902, p. 927. 



