336 EDWARD S. MORSE ON 



Hancock ('59) states that in the brachium he found 4,000 cirri. Whether this 

 number was based on a definite count or an estimate is not known. In the species 

 studied in the St. Lawrence, and which has always been recognized as identical with the 

 H. psittacea of Europe, I counted only 450 cirri on the brachium of a fully matured speci- 

 men. This leads me to believe that Hancock's figure is the result of a misprint and that 

 the number should read 400 and not 4,000. 



MUSCLES. 



The muscles of many forms of Brachiopoda have been often figured and described, 

 and a number of investigators have given their own interpretation of the functions of 

 these muscles with a terminology of their own, differing, of course, from that of their 

 predecessors. Hancock's names for the muscles of Liugula were vitiated because he 

 argued from analogy that since the Testicardme forms had an interlocking device to 

 prevent the lateral displacement of the shells, in Liugula, there being no such interlocking 

 device in the shells, the muscles were so arranged as to accomplish the same purpose. 

 He says, " Indeed the attachments of the various muscles [in Lingula] are so distributed 

 around the margin of the perivisceral chamber that transverse, longitudinal and diagonal 

 movements are alike guarded against. And perhaps their true functions are best 

 understood when thus considered in co-operation ; it is then seen that they form a com- 

 plicated complementary system for the purpose of assisting in adducting the valves, their 

 various points of attachment and different inclinations being so arranged, that, in what- 

 ever state of action they may happen to be, they will always keep the valves steadily and 

 accurately opposed to each other." In commenting on the names given by previous 

 investigators to the muscles of Liugula, Hancock says, " It is necessary to alter these later 

 epithets as they imply what appears to be a false theory, namely : the sliding of the valves 

 over each other." Owen ('35), to whose terminology he particularly refers and upon 

 which he animadverts, in describing the various muscles of Lingula, says, " The arrange- 

 ments of these powerful adductors are such as to effect the sliding movements of the 

 valves on each other, beside closing the shell, and to compress and variously affect the 

 interposed viscera and visceral lacunae with their contained sinuses," and I may add that 

 no words could express more correctly the precise work accomplished by these muscles, 

 for they cause not only the " transverse, longitudinal and diagonal movements " of the 

 shell, and that in a more vigorous way than even Owen dreamed of, but they do com- 

 press and variously affect the interspersed viscera and the circulation, as will be seen 

 farther on. 



