460 R. ETHERIDGE, JTTN., ON A LOWER-CARBONIFEROUS PRODUCTUS. 



the former. The spines of the ventral valve are wound round the 

 bodies of attachment in the most complete manner (fig. 1 &c), one 

 individual holding on by as few as two spines and a portion of a 

 third (fig. 11), another by six spines, and again another by seven, 

 and so on, sometimes singly (figs. 1, 2, 3, 5, &c), at other times in 

 clusters (fig. 4). When the organism to which the Productus is 

 attached is of larger size than the latter, the whole of the ventral 

 valve is applied to it, the spines spreading out and round on each 

 side (figs. 2, 4, 5) ; but when the foreign body is of less diameter 

 than the Productus, as is usually the case with fragments of Polyzoa, 

 several of the spines are wound tightly round, especially near the 

 beak, and the remainder of the valve remains free (figs. 1, 3, 11). 

 Attachment took place during the life of the Crinoid ; for, in nearly 

 every case where the Productus remains adhering, we find that its 

 rate of growth was less than that of the Crinoid, the result being 

 that the substance of the latter surrounded or enclosed its parasite, 

 first the encircling spines disappearing and gradually the shell 

 (figs. 6-10). We have specimens showing this remarkably well in 

 all stages of the process, from the mere absorption of the spines by 

 the substance of the Crinoid, up to the total disappearance of the 

 Productus itself, when the Crinoid stem assumes a swollen or dis- 

 torted appearance (fig. 10). From a consideration of this gradual 

 absorption by the Crinoid stem there arise two questions : — I)id the 

 Productus when once attached lose the power to free itself? or, Did 

 the absorption by the Crinoid, contrary to the view indicated pre- 

 viously, commence only after the death of the Productus ? To show 

 how closely these little shells congregated I have given a figure of 

 an Enerinite stem on which may be seen the grooves caused by the 

 removal of a number of the encircling spines (fig. 12). 



In the young state the characters of this hugging Productus are 

 obscure ; but in the mature (or what I take to be the mature) form 

 they become well marked and constant. In marginal outline the 

 shell somewhat resembles the P. aculeatus group, with the hinge-line 

 scarcely as long as the shell. The auricular expansions are well 

 marked but flattened (figs. 13, 14, 19), and the cardinal angles 

 sharp (figs. 13, 14). The ventral valve is slightly convex when the 

 individuals are partially free, and without sinus (figs. 13-15). The 

 dorsal is flat or a little concave (figs. 18, 19, 22, 24), and granular 

 on the interior surface. The cardinal process is bifid and broadly 

 Y-shaped (figs. 18, 21, 24), with strong lateral ridges proceeding 

 from it to the cardinal angles (a, figs. 21, 23). The mesial ridge in 

 the interior of the dorsal valve, immediately under the cardinal pro- 

 cess, is divided into two portions (b, figs. 21, 23), which unite at 

 about one third from the hinge-line, enclosing between them a 

 rather deep pit or space (c, figs. 21, 23), which partially represents 

 the convex visceral region of the shell externally. The mesial ridge 

 becomes stronger and more pronounced towards the front, and 

 divides the shell symmetrically. Both valves are covered with a 

 variable number of sharp, undulating, concentric wrinkles or corru- 

 gations, coarse for the size of the shell, and occasionally irregular 



