466 PROCEEDINGS OF THE ACADEMY OF 



united into a single plate, which expands on the sides and in front, forming a 

 bag-like cavity, attached by its outer surface to shells or rocks, and, as the 

 animal increases in size, it expands behind into a shelly tube with a circular 

 aperture. 



The front of the mantle is furnished with scattered tentacles, which are 

 emitted through tubular pores on the upper part of the front of the tube, and 

 round the circumference of the part by which it is attached. 



The shells are attached to the surface of shells or rocks, and not sunk into 

 their substance ; nor do the animals live sunk in the sand like Aspergillid>e 

 and GastrochjEnid;e. 



Genus Humphreyia. 



We have adopted several of the subfamilies and genera proposed by Dr. 

 Gray, and have also used some of the genera as subgenera, but we do not 

 consider the differences among these shells to be sufficient to warrant the 

 creation of three families ; nor are the genera so numerous as to require such 

 a division for their proper study. The families proposed by Dr. Gray are not 

 only discarded for the foregoing reasons, but also because their characters 

 are very unequal in value. The first, comprising shells with both valves free, 

 and those with but one valve free, the other attached, presents stronger dif- 

 ferences within itself than those by which he has separated it from the second 

 family; while the third (Humphreyiadje) is described as possessing a peculiar 

 mode of growth, the tube being an enlargement or prolongation of the shelly 

 valves. This may be true with regard to Humpreyiad^e, but then it is also 

 true of the genus Brechites, the depressions round the valves evidently marking 

 the growth of the tube from them, as a nucleus. 



Mr. Lovell Reeve, in his " Monograph of Aspergillum," says, in relation to 

 Humphreyia : 



"If the animal of this interesting form of Aspergillum could speak, its 

 remarks on Dr. Gray's ingenious description of its structure, habits and shell 

 would probably resemble those of our great landscape painter Turner, on the 

 criticisms of his pictures by Ruskin, ' Ah ! he sees a great deal more in them 

 than I can, or ever intended should be seen.' 



" The peculiarities of Aspergillum [Humphreyia) Strangei are, that it is an 

 adherent species; and, secondly, that it forms its sheath in a square. Like 

 the shell of all other adherent species of a genus, compared with those that 

 live free, the shell of A. Strangei has a very distorted growth, and the part 

 of the attachment being the most delicate part of the shell is the part most 

 distorted. One of the only two specimens known has, on ceasing its free 

 habit, commenced to attach itself within the hinge portion of a muscle ; the 

 other has been attached to stone, in a manner obviously even less commodious 

 to the symmetry of its growth ; and many of the points seized by Dr. Gray as 

 points of generic character are contortions arising out of these peculiar cir- 

 cumstances of habitation. The disk is smashed in as it were, and the frill is 

 pushed out at the edge of the place of attachment, and both are an irregular 

 heap of contortion." 



The three groups or subfamilies into which we have divided the recent 

 Gastrocilenid^e, following the arrangement given by H. and A. Adams, form 

 very natural divisions of equal value ; and the first three genera, also, are 

 founded on constant and very distinct characters ; but the division of the old 

 genus Aspergillum must be regarded as a purely artificial arrangement of a 

 large number of species into groups, in order to facilitate their study, which, 

 in a genus so subject to distortion and abnormal mode of growth, had become 

 very perplexing. These genera will probably undergo much modification 

 when we havea better knowledge of their animals, which at present are 

 almost unknown to us. 



Naturalists are not all agreed as to the application of Guettard's name 



[Dec. 



