490 BALANID.E. 



The Basis is thin and membranous ; it firmly adheres to the surface 

 of attachment. 



Scuta, nearly flat : the articular ridge is very prominent, and there 

 is a deep articular furrow both above and below; but the precise outline 

 of the ridge and furrows varies : there is a pit for the adductor muscle, 

 but no crests or marks for the other muscles. The Terga are remark- 

 able from the extreme prominence of the articular ridge and depth of 

 the articular furrow. The basal margin viewed internally seems 

 straight, so that there appears to be no spur ; but viewed externally, 

 when the crests for the depressor muscles are seen to depend con- 

 siderably beneath the true basal margin, a slight, very broad spur 

 may be perceived to exist. These depending crests for the muscles 

 are rather thin, but they extend over half the basal margin of the valve. 



Mouth. — Thelabrum is very bullate, being as long in its longitudinal 

 axis as the rest of the mouth : crest hairy, with some very minute teeth. 

 Palpi truncated, with their apices not nearly touching each other ; 

 thickly clothed with spines. Mandibles with three large single teeth, 

 of which the lower one has a single fine tooth at its upper basal edge, 

 showing a tendency to become pectinated ; inferior part short, coarsely 

 pectinated. Maxillae notched, with a slight second notch and slight 

 double prominence in the lower part. 



Cirri. — First and second pairs short, with the rami in each un- 

 equal in length by about four segments ; on both rami in the second 

 cirrus, and in the shorter ramus of the first cirrus, there are some 

 coarsely pectinated spines. All four posterior cirri are alike ; the 

 segments bear five pairs of strong spines, with a large intermediate 

 tuft of fine spines : the dorsal tuft is also large, consisting of short 

 thick, and long finer spines. There is no vestige of caudal appendages, 

 though present in the succeeding species. 



Branchiae moderately large, in area equalling the prosoma ; surface 

 not plicated. 



2. Catophragmus imbricatus. 



Catopuragmus imbricatus. G. B. Sowerby. Genera of Ptecent 



and Fossil Shells, Plate. 



Basis calcareous : caudal appendages present. 



Hah. — Antigua, West Indies, attached to a Tetraclita porosa. 



As stated under the genus, this species is known from two specimens 

 in the British Museum, one of which is full-sized, being three quarters 

 of an inch in diameter, but is destitute of the outermost whorls, of the 

 basis, opercular valves, and animal's body ; the other is perfect, but very 

 young, being barely two tenths of an inch in basal diameter. As far as 

 the characters can be made out from these materials, I can perceive 



