236 Report of the State Geologist. 



square appendages were formed either inside of the gonangium 

 or immediately after the detachment of the siculae. 



Some of the best specimens bearing these plates are figured on 

 PL III. Figure 1 represents the most common appearance of the 

 appendage as the impression of a square plate, slightly raised 

 in the center and sometimes with chitinous test; at the under 

 side of the plate is a small round node, from which the sicula 

 springs with a process of varying length. While the sides are 

 mostly convex, some specimens, in later growth stages, show 

 concave sides (fig. 2), perhaps the result of shrinkage of the still 

 tender organ. 



Figure 3 represents a specimen which is remarkable for show- 

 ing to the naked eye broad radial ribs, and for displaying under 

 the glass a series of fine concentric furrows and wrinkles around 

 the central node. The same regular concentric furrowing can be 

 observed on some older and larger plates (PL III, figs. 9, 13, 14). 

 It excludes, by its regularity, the idea that it might be the result 

 of shrinkage, or of the flattening of the bladder-like body. 



In seeking an homology of the ht rny cone or sicula, among 

 the growth stages of a Sertularian colony, we shall be embar- 

 rassed by the very fact of the chitinous nature of this embry- 

 onic sheath. The horny receptacle of the Sertularians, called 

 gonangium, produces embryos without a horny perisarc, while 

 that of Diplograptus produces such with a horny perisarc. And 

 yet, there is a more than superficial similitude between the 

 sicula of Dij)lograptus and the primary polypite of the Sertu- 

 larians, which is borne on a short hydrocaulus, fastened by a 

 round disc to the bottom and produces the first hydrotheca, 

 whence the whole colony arises by lateral budding (cf. AUmann, 

 1. c). Supposing this polypite and its disc to be clad from the 

 beginning in the horny perisarc by which the colony begins 

 to protect itself in a little more advanced stage, there would 

 result a first stage of growth strikingly similar to that of 

 Diplograptus ; there would be a primary theca, a hydrocaulus, 

 a basal appendage and a lateral budding of the first hydrotheca. 

 The earlier beginning of the secretion of the perisarc with 

 the embryo of Biplograptus can not be regarded as of princi- 

 pal importance, but there exists a distinctive feature of great 



