so-called u Farrzngdon Sponges. 71 23 



In diameter the filiform spicules somewhat vary above and 

 I below the four-thousandth part of an inch, which is much 



beyond that of the arms of many triradiates in existing Calci- 

 sponges ; but, from their long and flexuous course, subjecting 

 them to truncation in a thin slice I have only been able to 

 find one or two instances of an attenuated natural termination, 

 and that, too, only at one end of the fragment. Instances are 

 not uncommon where they may be inferred to terminate in 

 this way in one direction, viz. in a point ; but this may be so 

 simulated by oblique-sectioning or descending out of focus, 

 that it would be hazardous to go beyond an opinion in the 

 matter. On the other hand, there is also often evidence of 

 simple or multiple division, as in Peronella dumosa, from Far- 

 ringdon ('Handbuch der Palaeontologie,' Zittel,p. 190, fig. 108), 

 wherein the filament may be observed to divide into two or 

 more arms radiating from the same point, one or more of 

 which may be elongated beyond tracing (t. e. filiform), or one 

 or more short and pointed, mixed with regular or equiarmed 

 triradiates that are free ; but it is often impossible to substan- 

 tiate this, from the presence of the flocculent material produced 

 by the fossilization giving rise to a cloudiness in the fibre, 

 which obscures the very part which it seems desirable to be 

 able to follow with certainty ; in short, it is only by the 

 happy coincidence of a sharply defined object occurring in a 

 clear place that such a point can be satisfactorily determined. 

 Difficult, however, as it is to follow the a filiform " spicules 

 to their extremities in the fossils above mentioned, chiefly 

 from their great length and undulating course, a key to their 

 interpretation seems to be afforded by the fibre of Prof. ZitteFs 

 preparation of Peronella multidigitata (to which I have alluded) , 

 wherein, being of the same kind but shorter, they can be 

 clearly seen to be the arms of a triradiate. Perhaps this 

 slice may have been taken from an unusually favourable 

 * . specimen for the purpose ; but be that as it may, not only this 

 < identity, but an identity in form and arrangement between the 



I triradiates themselves and those of existing Calcisponges can 



be witnessed, as I have before mentioned. It is true that in 

 many instances the third ray is more or less reduced by arrest 

 of development to a mere tubercle, as pointed out by Dr. 

 Hinde in his Verticillites D 1 Orbignyi (No. 14, p. 193, pi. xi. 

 figs. 15-22, &c.) ; yet in many cases all three rays are perfect 





and unmistakable in their form and arrangement. 



As regards the u colossal " spicules (a term borrowed from 

 Hackel in existing species) of the axis, so well shovjn in Dr. 

 Hinde's illustration of the fibre of his Sestrostomella rugosa 

 (Xo. 14, pi. xii. fig. 1, a), all that I need say after an exami- 



