ANIMALS. 101 



plate by figures 20, 21, 22, 23, 24, 25, 29, 30): possibly they are specifically 

 distinct :^ and it is this idea which causes me to be particular in stating, that the 

 Tunstall Hill form must be considered as the type of the species. The variety 

 Humbletonensis appears to graduate the latter into the Strophalosia Cancrini, which, 

 however, in addition to the other distinguishing characters already noticed, has its 

 large valve too much vaulted to be confounded with the form in question. 



Strophalosia Morrisiana, considered in all its modifications, may be readily 

 distinguished from the two species last described. It is decidedly more regular in 

 form than 8. Goldfussi ; and the area, although wider, is not so high (vide PI. XII, 

 fig. 19) : the spines too, are not so numerous. It agrees with S. excavata in form and 

 in the size of the area ;^ but in this species the spines are far more numerous and more 

 regular in their arrangement ; though in the latter respect there is a simulation on the 

 part of 8. Morrisiana. The present one differs from both species in having the valves 

 striated, and the spines adpressed. 



There is a singular peculiarity in this species requiring to be mentioned. I have 

 seen several specimens of the rounded variety, found at Humbleton Gluany, appearing 

 as if trivalved ; but whether it is due to accidental circumstances I am not prepared to 

 say : its occurrence in several specimens seems to negative this conclusion. I have 

 had represented in Plate XII, figs. 20, 21, 22, 23, 24, two of my specimens displaying 

 this character ; leaving it to be cleared up by future researches. Full grown 

 specimens of the same variety occasionally show the anterior margins arching and 

 gaping so as to approximate to the form of the circular or elliptical orifice of Produdus 

 joroboscideus before its tube becomes developed. I still think that this singular 

 modification has been caused by the flowing in and out of the currents which supplied 

 the mollusc with the necessary quantity of nutriment and fresh air.^ 



In making the Orthothrix lamellosus of Geinitz synonymous wdth this species, 

 notwithstanding the former is stated to be without spines on the small valve, I have 

 been influenced by certain of my specimens displaying lamellae on this valve somewhat 

 similar to those represented in the ' Versteinerungen,' at figures 1 5 «, 16, 1 7 «, 2 1 , 

 in Plate V. The fossHs identified by Dr. Geinitz (vide PI. VI, figs. 16, 17, 18) with the 

 Strophalosia Cancrini, I readily recognise as belonging to 8. Morrisiana. 



' I designate the Humbleton form Strophalosia Morrisiana, var. Humbletonensis : in case it should be 

 found to be a distinct species, the varietal may be conveniently used for the specific name. 



^ The area is represented too high by nearly one half in the restored medio-longitudinal section repre- 

 sented in Plate XI, fig. 2 1 ; further, the spines are too much elevated, and the large valve is rather too 

 convex for the typical form. 



3 " Koninck, from an examination of Productus proboscideus, supposes that it (the genus generally) 

 was attached by means of fibres passing out of the anterior opening, which would compel us to conclude 

 that the genus did not belong to the Palliobranchiata. Instead of the anterior tubular opening of 

 P. proboscideus subserving such an office, I cannot but think that it simply served as a passage for the 

 ingress and egress currents." (Vide Annals and Mag. of Nat. Hist., vol. xxiii, p. 93.) 



