On CalamoporcB in gravel deposits near Ann Arbor, Mich. 391 



Striatopora is separated on account of its having longitudinal 

 striae on the inside of its tubes, but this character is essential to 

 Calamopora and to all its sub-genera. In some specimens or 

 species this striation is somewhat obscure, but this does not alter 

 the general rule. 



Michelinia includes Calamopor^e with very large tubes and 

 compound vesicular diaphragms. The longitudinal striae in its 

 tubes are more numerous than in other Calamoporte and the 

 side pores are remarkably small and irregularly disseminated. 



The separate tubes of some corals, connected by lateral pro- 

 cesses and with constrictions at various intervals, named by Bil- 

 lings HaimeophyUuvi, under certain circumstances coalesce, and 

 become connected by lateral pores, assuming altogether the form 

 of a Michelinia. 



Some other subgenera have been dissevered from Calamopora 

 without any proper justification. 



Emmonsia is characterized by tubes in which the ordinary 

 simple diaphragms are in part or wholly replaced by compound 

 and imperfectly developed diaphragms. This character is so 

 little constant that, in the same tubes, a succession of perfectly 

 regular simple diaphragms may be observed, while in previous 

 or subsequent periods of growth only compound and partial dia- 

 phragms were deposited. 



Astrocerium is not entitled to more credit; it is based upon the 

 presence of rows of spinules on the inner surface of its tubes. 

 Spiiiules are decorative organs, noticed in a number of other 

 Calamopone, which the author allows to bear their old name ; 

 these spinules are also not equally well developed in all speci- 

 iJiens of the same species and are often obliterated by the effects 

 of petrification. 



A character upon which alone a generic distmction is based 

 should not be subject to obliteration by want of development 

 or by the effects of petrification. . 



Before entering upon a detailed description of species, I have to 

 make some remarks upon the value of the number and disposi- 

 tion of the lateral pores, for specific distinction. It is desirable, 

 that each species of Calamopora should have certain peculiar 

 features, with regard to the size, number and disposition of its 

 lateral pores, which can serve as subordinate characters, for dis- 

 tinction of one kind from the other, but most writers have placed 

 too much importance upon these characters. The tubes of a Cal- 

 amopora form irregular polygons, which of itself excludes a reg- 

 ularity in the number of pore-ro^s on a side ; but suppose the 

 polygons were regular— the number of rows m a species does not 

 seem to be constant, for the circumference of a tube. 



The same want 6i precision exists with regard to the position 

 of pores on the sides or on the angles. 



