HAMBACH — STRUCTURE * CLASSIFICAITON OF PENTREMITES. 547 



Roemer, which has been in use for some time, whereas the insuf- 

 ficiency of Shumard's will speak for itself ; and, as long- as we 

 do not know of anything better, such a classification should be 

 abandoned, as it would only increase our nomenclature with un- 

 necessary synonyms. The mere recapitulation of what has been 

 done by others is of very little value, even if a different termin- 

 ology is used for it. 



The condition of life was undoubtedly a similar one through- 

 out the whole class, therefore it cannot very well be called an 

 arbitrary assumption to suppose the presence of certain organs 

 with the same physiological functions in all these animals. The 

 absence or nondetection of either one of them is certainly due to 

 an insuflficient state of preservation ; for the greatest number of 

 specimens of those species is found in an imperfect state of pre- 

 servation, but is no evidence that they were never in the posses- 

 sion of them. 



The exoskeleton, i.e. the calcareous parts forming the calyx, 

 as also the relative position of each, is the same in all Pentre- 

 mites as well as in those recently separated from them (whether 

 they are of a globose, truncate or clavate form, with small or 

 broad ambulacral fields), and is certainly of far greater import- 

 ance than the mere softer interior organs to which belong the 

 hydrospiric sac and other vessels. The calcareous portion of 

 the ambulacral field consists only of lancet pieces and poral pieces. 



It is arbitrary and without any good reason to form of a cer- 

 tain number of species a new genus* because their base plates 

 are small and depressed or elongated, or having a narrow, short 

 or long sinus in the fork pieces, which, if such is the case, must 

 necessarily give a difterent aspect to the individual, and cause 

 them to be respectively either globose, elliptical, pyriform, or 

 clavate, which forms are met with in both those having a broad 

 or narrow ambulacral field. The number of hydrospiric plicas 

 can hardly be of any consequence as shown above. Carpenter 

 reports Pentremites Reimvardtii as having three plicas, whereas 

 I have specimens which possess five, and others possessing a dif- 

 ferent number, in the same specimen. 



* See Carpenter, loc. cit. 



